keyctl

KEYCTL(2)                 Linux Key Management Calls                 KEYCTL(2)

NAME
       keyctl - manipulate the kernel's key management facility

SYNOPSIS
       #include <sys/types.h>
       #include <keyutils.h>

       long keyctl(int operation, ...)

       /* For direct call via syscall(2): */
       #include <asm/unistd.h>
       #include <linux/keyctl.h>
       #include <unistd.h>

       long syscall(__NR_keyctl, int operation, __kernel_ulong_t arg2,
                    __kernel_ulong_t arg3, __kernel_ulong_t arg4,
                    __kernel_ulong_t arg5);

       No glibc wrapper is provided for this system call; see NOTES.

DESCRIPTION
       keyctl() allows user-space programs to perform key manipulation.

       The  operation  performed by keyctl() is determined by the value of the
       operation argument.   Each  of  these  operations  is  wrapped  by  the
       libkeyutils  library (provided by the keyutils package) into individual
       functions (noted below) to permit the compiler to check types.

       The permitted values for operation are:

       KEYCTL_GET_KEYRING_ID (since Linux 2.6.10)
              Map a special key ID to a real key ID for this process.

              This operation looks up the special key whose ID is provided  in
              arg2  (cast  to key_serial_t).  If the special key is found, the
              ID of the corresponding real key is  returned  as  the  function
              result.  The following values may be specified in arg2:

              KEY_SPEC_THREAD_KEYRING
                     This   specifies  the  calling  thread's  thread-specific
                     keyring.  See thread-keyring(7).

              KEY_SPEC_PROCESS_KEYRING
                     This specifies  the  caller's  process-specific  keyring.
                     See process-keyring(7).

              KEY_SPEC_SESSION_KEYRING
                     This  specifies  the  caller's  session-specific keyring.
                     See session-keyring(7).

              KEY_SPEC_USER_KEYRING
                     This specifies the caller's  UID-specific  keyring.   See
                     user-keyring(7).

              KEY_SPEC_USER_SESSION_KEYRING
                     This  specifies  the  caller's  UID-session keyring.  See
                     user-session-keyring(7).

              KEY_SPEC_REQKEY_AUTH_KEY (since Linux 2.6.16)
                     This  specifies  the   authorization   key   created   by
                     request_key(2)  and  passed  to  the process it spawns to
                     generate a key.  This key is available only in a request-
                     key(8)-style program that was passed an authorization key
                     by the  kernel  and  ceases  to  be  available  once  the
                     requested key has been instantiated; see request_key(2).

              KEY_SPEC_REQUESTOR_KEYRING (since Linux 2.6.29)
                     This specifies the key ID for the request_key(2) destina-
                     tion keyring.   This  keyring  is  available  only  in  a
                     request-key(8)-style  program  that  was passed an autho-
                     rization key by the kernel and  ceases  to  be  available
                     once   the  requested  key  has  been  instantiated;  see
                     request_key(2).

              The behavior if the key specified in arg2 does not exist depends
              on  the value of arg3 (cast to int).  If arg3 contains a nonzero
              value, then--if it is appropriate to do so (e.g.,  when  looking
              up the user, user-session, or session key)--a new key is created
              and its real key ID returned as the function result.  Otherwise,
              the operation fails with the error ENOKEY.

              If a valid key ID is specified in arg2, and the key exists, then
              this operation simply returns the key ID.  If the key  does  not
              exist, the call fails with error ENOKEY.

              The caller must have search permission on a keyring in order for
              it to be found.

              The arguments arg4 and arg5 are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_get_keyring_ID(3).

       KEYCTL_JOIN_SESSION_KEYRING (since Linux 2.6.10)
              Replace  the  session  keyring this process subscribes to with a
              new session keyring.

              If arg2 is NULL,  an  anonymous  keyring  with  the  description
              "_ses"  is created and the process is subscribed to that keyring
              as its session keyring, displacing the previous session keyring.

              Otherwise, arg2 (cast to char *) is treated as  the  description
              (name) of a keyring, and the behavior is as follows:

              *  If  a keyring with a matching description exists, the process
                 will attempt to subscribe to  that  keyring  as  its  session
                 keyring  if  possible;  if  that is not possible, an error is
                 returned.  In order to subscribe to the keyring,  the  caller
                 must have search permission on the keyring.

              *  If a keyring with a matching description does not exist, then
                 a new keyring with the specified description is created,  and
                 the  process  is  subscribed  to  that keyring as its session
                 keyring.

              The arguments arg3, arg4, and arg5 are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_join_session_keyring(3).

       KEYCTL_UPDATE (since Linux 2.6.10)
              Update a key's data payload.

              The arg2 argument (cast to key_serial_t) specifies the ID of the
              key to be updated.  The arg3 argument (cast to void *) points to
              the  new payload and arg4 (cast to size_t) contains the new pay-
              load size in bytes.

              The caller must have write permission on the key  specified  and
              the key type must support updating.

              A   negatively   instantiated   key   (see  the  description  of
              KEYCTL_REJECT) can be positively instantiated with  this  opera-
              tion.

              The arg5 argument is ignored.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_update(3).

       KEYCTL_REVOKE (since Linux 2.6.10)
              Revoke  the  key  with  the  ID  provided  in  arg2   (cast   to
              key_serial_t).   The key is scheduled for garbage collection; it
              will no longer be findable, and will be unavailable for  further
              operations.   Further attempts to use the key will fail with the
              error EKEYREVOKED.

              The caller must have write or setattr permission on the key.

              The arguments arg3, arg4, and arg5 are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_revoke(3).

       KEYCTL_CHOWN (since Linux 2.6.10)
              Change the ownership (user and group ID) of a key.

              The  arg2  argument  (cast to key_serial_t) contains the key ID.
              The arg3 argument (cast to uid_t) contains the new user  ID  (or
              -1 in case the user ID shouldn't be changed).  The arg4 argument
              (cast to gid_t) contains the new group ID (or  -1  in  case  the
              group ID shouldn't be changed).

              The key must grant the caller setattr permission.

              For  the  UID  to  be changed, or for the GID to be changed to a
              group the caller is not a member of, the caller  must  have  the
              CAP_SYS_ADMIN capability (see capabilities(7)).

              If  the  UID is to be changed, the new user must have sufficient
              quota to accept the key.  The quota deduction  will  be  removed
              from the old user to the new user should the UID be changed.

              The arg5 argument is ignored.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_chown(3).

       KEYCTL_SETPERM (since Linux 2.6.10)
              Change the permissions of the key with the ID  provided  in  the
              arg2 argument (cast to key_serial_t) to the permissions provided
              in the arg3 argument (cast to key_perm_t).

              If the caller doesn't have the CAP_SYS_ADMIN capability, it  can
              change  permissions only for the keys it owns.  (More precisely:
              the caller's filesystem UID must match the UID of the key.)

              The key must grant setattr permission to the  caller  regardless
              of the caller's capabilities.

              The  permissions  in  arg3 specify masks of available operations
              for each of the following user categories:

              possessor (since Linux 2.6.14)
                     This is the permission granted to  a  process  that  pos-
                     sesses  the key (has it attached searchably to one of the
                     process's keyrings); see keyrings(7).

              user   This  is  the  permission  granted  to  a  process  whose
                     filesystem UID matches the UID of the key.

              group  This  is  the  permission  granted  to  a  process  whose
                     filesystem GID or any of its supplementary  GIDs  matches
                     the GID of the key.

              other  This is the permission granted to other processes that do
                     not match the user and group categories.

              The user, group,  and  other  categories  are  exclusive:  if  a
              process  matches  the user category, it will not receive permis-
              sions granted in the group category; if a  process  matches  the
              user  or  group  category,  then it will not receive permissions
              granted in the other category.

              The possessor category grants permissions  that  are  cumulative
              with the grants from the user, group, or other category.

              Each  permission  mask is eight bits in size, with only six bits
              currently used.  The available permissions are:

              view   This permission allows reading attributes of a key.

                     This permission is required for the KEYCTL_DESCRIBE oper-
                     ation.

                     The  permission  bits for each category are KEY_POS_VIEW,
                     KEY_USR_VIEW, KEY_GRP_VIEW, and KEY_OTH_VIEW.

              read   This permission allows reading a key's payload.

                     This permission is required for  the  KEYCTL_READ  opera-
                     tion.

                     The  permission  bits for each category are KEY_POS_READ,
                     KEY_USR_READ, KEY_GRP_READ, and KEY_OTH_READ.

              write  This permission allows update or instantiation of a key's
                     payload.   For a keyring, it allows keys to be linked and
                     unlinked from the keyring,

                     This  permission  is  required  for  the   KEYCTL_UPDATE,
                     KEYCTL_REVOKE,     KEYCTL_CLEAR,     KEYCTL_LINK,     and
                     KEYCTL_UNLINK operations.

                     The permission bits for each category are  KEY_POS_WRITE,
                     KEY_USR_WRITE, KEY_GRP_WRITE, and KEY_OTH_WRITE.

              search This  permission  allows keyrings to be searched and keys
                     to be found.   Searches  can  recurse  only  into  nested
                     keyrings that have search permission set.

                     This      permission      is     required     for     the
                     KEYCTL_GET_KEYRING_ID,       KEYCTL_JOIN_SESSION_KEYRING,
                     KEYCTL_SEARCH, and KEYCTL_INVALIDATE operations.

                     The permission bits for each category are KEY_POS_SEARCH,
                     KEY_USR_SEARCH, KEY_GRP_SEARCH, and KEY_OTH_SEARCH.

              link   This permission allows a key or keyring to be linked to.

                     This permission  is  required  for  the  KEYCTL_LINK  and
                     KEYCTL_SESSION_TO_PARENT operations.

                     The  permission  bits for each category are KEY_POS_LINK,
                     KEY_USR_LINK, KEY_GRP_LINK, and KEY_OTH_LINK.

              setattr (since Linux 2.6.15).
                     This permission allows a key's UID, GID, and  permissions
                     mask to be changed.

                     This   permission  is  required  for  the  KEYCTL_REVOKE,
                     KEYCTL_CHOWN, and KEYCTL_SETPERM operations.

                     The   permission   bits    for    each    category    are
                     KEY_POS_SETATTR,  KEY_USR_SETATTR,  KEY_GRP_SETATTR,  and
                     KEY_OTH_SETATTR.

              As a convenience, the following macros are defined as masks  for
              all  of  the  permission  bits  in  each of the user categories:
              KEY_POS_ALL, KEY_USR_ALL, KEY_GRP_ALL, and KEY_OTH_ALL.

              The arg4 and arg5 arguments are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_setperm(3).

       KEYCTL_DESCRIBE (since Linux 2.6.10)
              Obtain a string describing the attributes of a specified key.

              The  ID of the key to be described is specified in arg2 (cast to
              key_serial_t).  The descriptive string is returned in the buffer
              pointed to by arg3 (cast to char *); arg4 (cast to size_t) spec-
              ifies the size of that buffer in bytes.

              The key must grant the caller view permission.

              The returned string is null-terminated and contains the  follow-
              ing information about the key:

                  type;uid;gid;perm;description

              In  the above, type and description are strings, uid and gid are
              decimal strings, and perm is  a  hexadecimal  permissions  mask.
              The descriptive string is written with the following format:

                  %s;%d;%d;%08x;%s

              Note:  the  intention  is  that the descriptive string should be
              extensible  in  future  kernel  versions.   In  particular,  the
              description  field  will  not  contain  semicolons; it should be
              parsed by working backwards from the end of the string  to  find
              the  last  semicolon.   This  allows  future semicolon-delimited
              fields to be inserted in the descriptive string in the future.

              Writing to the buffer is attempted only when  arg3  is  non-NULL
              and  the  specified  buffer  size  is large enough to accept the
              descriptive string (including the terminating  null  byte).   In
              order  to determine whether the buffer size was too small, check
              to see if the return value of  the  operation  is  greater  than
              arg4.

              The arg5 argument is ignored.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_describe(3).

       KEYCTL_CLEAR
              Clear the contents of (i.e., unlink all keys from) a keyring.

              The ID of the key (which must be of keyring type) is provided in
              arg2 (cast to key_serial_t).

              The caller must have write permission on the keyring.

              The arguments arg3, arg4, and arg5 are ignored.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_clear(3).

       KEYCTL_LINK (since Linux 2.6.10)
              Create a link from a keyring to a key.

              The  key  to  be  linked  is  specified   in   arg2   (cast   to
              key_serial_t);  the  keyring  is  specified  in  arg3  (cast  to
              key_serial_t).

              If a key with the same type and description is already linked in
              the keyring, then that key is displaced from the keyring.

              Before  creating  the link, the kernel checks the nesting of the
              keyrings and returns appropriate errors if the link  would  pro-
              duce  a  cycle  or  if the nesting of keyrings would be too deep
              (The limit on the nesting of keyrings is determined by the  ker-
              nel constant KEYRING_SEARCH_MAX_DEPTH, defined with the value 6,
              and is necessary to prevent overflows on the kernel  stack  when
              recursively searching keyrings).

              The  caller must have link permission on the key being added and
              write permission on the keyring.

              The arguments arg4 and arg5 are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_link(3).

       KEYCTL_UNLINK (since Linux 2.6.10)
              Unlink a key from a keyring.

              The  ID  of the key to be unlinked is specified in arg2 (cast to
              key_serial_t); the ID of the keyring from  which  it  is  to  be
              unlinked is specified in arg3 (cast to key_serial_t).

              If  the  key  is not currently linked into the keyring, an error
              results.

              The caller must have write permission on the keyring from  which
              the key is being removed.

              If  the  last  link  to  a key is removed, then that key will be
              scheduled for destruction.

              The arguments arg4 and arg5 are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_unlink(3).

       KEYCTL_SEARCH (since Linux 2.6.10)
              Search for a key in a keyring tree, returning its ID and option-
              ally linking it to a specified keyring.

              The tree to be searched is specified by passing the  ID  of  the
              head keyring in arg2 (cast to key_serial_t).  The search is per-
              formed breadth-first and recursively.

              The arg3 and arg4 arguments specify the key to be searched  for:
              arg3  (cast  as char *) contains the key type (a null-terminated
              character string up to 32 bytes in size, including the terminat-
              ing  null byte), and arg4 (cast as char *) contains the descrip-
              tion of the key (a null-terminated character string up  to  4096
              bytes in size, including the terminating null byte).

              The  source  keyring must grant search permission to the caller.
              When performing the recursive search, only keyrings  that  grant
              the  caller  search permission will be searched.  Only keys with
              for which the caller has search permission can be found.

              If the key is found, its ID is returned as the function result.

              If the key is found and arg5 (cast to key_serial_t) is  nonzero,
              then,  subject to the same constraints and rules as KEYCTL_LINK,
              the key is linked into the keyring  whose  ID  is  specified  in
              arg5.  If the destination keyring specified in arg5 already con-
              tains a link to a key that has the same  type  and  description,
              then  that  link will be displaced by a link to the key found by
              this operation.

              Instead of valid existing keyring IDs,  the  source  (arg2)  and
              destination  (arg5)  keyrings  can be one of the special keyring
              IDs listed under KEYCTL_GET_KEYRING_ID.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_search(3).

       KEYCTL_READ (since Linux 2.6.10)
              Read the payload data of a key.

              The  ID  of  the key whose payload is to be read is specified in
              arg2 (cast to key_serial_t).  This can be the ID of an  existing
              key,    or   any   of   the   special   key   IDs   listed   for
              KEYCTL_GET_KEYRING_ID.

              The payload is placed in the buffer pointed  by  arg3  (cast  to
              char *); the size of that buffer must be specified in arg4 (cast
              to size_t).

              The returned data will be processed for  presentation  according
              to the key type.  For example, a keyring will return an array of
              key_serial_t entries representing the IDs of all the  keys  that
              are linked to it.  The user key type will return its data as is.
              If a key type does not implement this  function,  the  operation
              fails with the error EOPNOTSUPP.

              If  arg3 is not NULL, as much of the payload data as will fit is
              copied into the buffer.  On  a  successful  return,  the  return
              value  is  always the total size of the payload data.  To deter-
              mine whether the buffer was of sufficient  size,  check  to  see
              that  the  return  value is less than or equal to the value sup-
              plied in arg4.

              The key must either grant the caller read permission,  or  grant
              the  caller search permission when searched for from the process
              keyrings (i.e., the key is possessed).

              The arg5 argument is ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_read(3).

       KEYCTL_INSTANTIATE (since Linux 2.6.10)
              (Positively)  instantiate an uninstantiated key with a specified
              payload.

              The ID of the key to be instantiated is provided in  arg2  (cast
              to key_serial_t).

              The  key  payload  is specified in the buffer pointed to by arg3
              (cast to void *); the size of that buffer is specified  in  arg4
              (cast to size_t).

              The  payload  may be a NULL pointer and the buffer size may be 0
              if this is supported by the key type (e.g., it is a keyring).

              The operation may be fail if the payload data is  in  the  wrong
              format or is otherwise invalid.

              If  arg5 (cast to key_serial_t) is nonzero, then, subject to the
              same constraints and rules as KEYCTL_LINK, the instantiated  key
              is linked into the keyring whose ID specified in arg5.

              The caller must have the appropriate authorization key, and once
              the uninstantiated key has been instantiated, the  authorization
              key  is  revoked.   In  other words, this operation is available
              only from a request-key(8)-style  program.   See  request_key(2)
              for an explanation of uninstantiated keys and key instantiation.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_instantiate(3).

       KEYCTL_NEGATE (since Linux 2.6.10)
              Negatively instantiate an uninstantiated key.

              This operation is equivalent to the call:

                  keyctl(KEYCTL_REJECT, arg2, arg3, ENOKEY, arg4);

              The arg5 argument is ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_negate(3).

       KEYCTL_SET_REQKEY_KEYRING (since Linux 2.6.13)
              Set  the default keyring to which implicitly requested keys will
              be linked for this thread,  and  return  the  previous  setting.
              Implicit  key  requests are those made by internal kernel compo-
              nents, such as can occur when, for example, opening files on  an
              AFS  or NFS filesystem.  Setting the default keyring also has an
              effect when requesting a key from user space; see request_key(2)
              for details.

              The  arg2  argument (cast to int) should contain one of the fol-
              lowing values, to specify the new default keyring:

              KEY_REQKEY_DEFL_NO_CHANGE
                     Don't change the default keyring.  This can  be  used  to
                     discover  the  current  default keyring (without changing
                     it).

              KEY_REQKEY_DEFL_DEFAULT
                     This selects the default behaviour, which is to  use  the
                     thread-specific  keyring  if  there is one, otherwise the
                     process-specific keyring if there is one,  otherwise  the
                     session  keyring  if there is one, otherwise the UID-spe-
                     cific  session  keyring,  otherwise   the   user-specific
                     keyring.

              KEY_REQKEY_DEFL_THREAD_KEYRING
                     Use  the  thread-specific  keyring (thread-keyring(7)) as
                     the new default keyring.

              KEY_REQKEY_DEFL_PROCESS_KEYRING
                     Use the process-specific keyring (process-keyring(7))  as
                     the new default keyring.

              KEY_REQKEY_DEFL_SESSION_KEYRING
                     Use  the session-specific keyring (session-keyring(7)) as
                     the new default keyring.

              KEY_REQKEY_DEFL_USER_KEYRING
                     Use the UID-specific keyring (user-keyring(7)) as the new
                     default keyring.

              KEY_REQKEY_DEFL_USER_SESSION_KEYRING
                     Use   the  UID-specific  session  keyring  (user-session-
                     keyring(7)) as the new default keyring.

              KEY_REQKEY_DEFL_REQUESTOR_KEYRING (since Linux 2.6.29)
                     Use the requestor keyring.

              All other values are invalid.

              The arguments arg3, arg4, and arg5 are ignored.

              The setting controlled by this operation  is  inherited  by  the
              child of fork(2) and preserved across execve(2).

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_set_reqkey_keyring(3).

       KEYCTL_SET_TIMEOUT (since Linux 2.6.16)
              Set a timeout on a key.

              The ID of the key is specified in arg2 (cast  to  key_serial_t).
              The  timeout  value, in seconds from the current time, is speci-
              fied in arg3 (cast to unsigned int).  The  timeout  is  measured
              against the realtime clock.

              Specifying the timeout value as 0 clears any existing timeout on
              the key.

              The /proc/keys file displays the remaining time until  each  key
              will  expire.  (This is the only method of discovering the time-
              out on a key.)

              The caller must either have the setattr permission on the key or
              hold  an  instantiation  authorization  token  for  the key (see
              request_key(2)).

              The key and any links to the key will be  automatically  garbage
              collected  after  the  timeout  expires.  Subsequent attempts to
              access the key will then fail with the error EKEYEXPIRED.

              This operation cannot  be  used  to  set  timeouts  on  revoked,
              expired, or negatively instantiated keys.

              The arguments arg4 and arg5 are ignored.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_set_timeout(3).

       KEYCTL_ASSUME_AUTHORITY (since Linux 2.6.16)
              Assume (or divest) the  authority  for  the  calling  thread  to
              instantiate a key.

              The  arg2  argument  (cast  to  key_serial_t) specifies either a
              nonzero key ID to assume authority, or the  value  0  to  divest
              authority.

              If  arg2  is nonzero, then it specifies the ID of an uninstanti-
              ated key for which authority is to be  assumed.   That  key  can
              then   be   instantiated   using   one   of  KEYCTL_INSTANTIATE,
              KEYCTL_INSTANTIATE_IOV, KEYCTL_REJECT, or  KEYCTL_NEGATE.   Once
              the  key  has  been  instantiated,  the  thread is automatically
              divested of authority to instantiate the key.

              Authority over a key can be assumed only if the  calling  thread
              has  present in its keyrings the authorization key that is asso-
              ciated  with  the  specified  key.    (In   other   words,   the
              KEYCTL_ASSUME_AUTHORITY  operation  is  available  only  from  a
              request-key(8)-style program; see request_key(2) for an explana-
              tion  of  how  this  operation  is  used.)  The caller must have
              search permission on the authorization key.

              If the specified key has a matching authorization key, then  the
              ID  of  that key is returned.  The authorization key can be read
              (KEYCTL_READ)  to  obtain  the  callout  information  passed  to
              request_key(2).

              If the ID given in arg2 is 0, then the currently assumed author-
              ity is cleared (divested), and the value 0 is returned.

              The KEYCTL_ASSUME_AUTHORITY mechanism allows a program  such  as
              request-key(8)  to assume the necessary authority to instantiate
              a new uninstantiated key that was created as a consequence of  a
              call   to   request_key(2).    For   further   information,  see
              request_key(2) and the kernel  source  file  Documentation/secu-
              rity/keys-request-key.txt.

              The arguments arg3, arg4, and arg5 are ignored.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_assume_authority(3).

       KEYCTL_GET_SECURITY (since Linux 2.6.26)
              Get the LSM (Linux Security Module) security label of the speci-
              fied key.

              The ID of the key whose security label is to be fetched is spec-
              ified in arg2 (cast to key_serial_t).  The security label  (ter-
              minated  by a null byte) will be placed in the buffer pointed to
              by arg3 argument (cast to char *); the size of the  buffer  must
              be provided in arg4 (cast to size_t).

              If  arg3  is  specified  as NULL or the buffer size specified in
              arg4 is too small, the full size of the  security  label  string
              (including  the  terminating null byte) is returned as the func-
              tion result, and nothing is copied to the buffer.

              The caller must have view permission on the specified key.

              The returned security label string will be rendered  in  a  form
              appropriate  to the LSM in force.  For example, with SELinux, it
              may look like:

                  unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

              If no LSM is currently in force, then an empty string is  placed
              in the buffer.

              The arg5 argument is ignored.

              This  operation  is  exposed  by  libkeyutils  via the functions
              keyctl_get_security(3) and keyctl_get_security_alloc(3).

       KEYCTL_SESSION_TO_PARENT (since Linux 2.6.32)
              Replace the session keyring to which the parent of  the  calling
              process  subscribes  with  the  session  keyring  of the calling
              process.

              The keyring will be replaced in the parent process at the  point
              where  the  parent  next  transitions  from kernel space to user
              space.

              The keyring must exist and must grant the  caller  link  permis-
              sion.   The  parent process must be single-threaded and have the
              same effective ownership as this process and must  not  be  set-
              user-ID or set-group-ID.  The UID of the parent process's exist-
              ing session keyring (f it has one), as well as the  UID  of  the
              caller's session keyring much match the caller's effective UID.

              The  fact that it is the parent process that is affected by this
              operation allows a program such as the shell to  start  a  child
              process  that  uses this operation to change the shell's session
              keyring.  (This is what the keyctl(1) new_session command does.)

              The arguments arg2, arg3, arg4, and arg5 are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_session_to_parent(3).

       KEYCTL_REJECT (since Linux 2.6.39)
              Mark  a  key  as  negatively  instantiated and set an expiration
              timer on the key.  This operation provides  a  superset  of  the
              functionality of the earlier KEYCTL_NEGATE operation.

              The ID of the key that is to be negatively instantiated is spec-
              ified in  arg2  (cast  to  key_serial_t).   The  arg3  (cast  to
              unsigned  int)  argument  specifies  the lifetime of the key, in
              seconds.  The arg4 argument (cast to unsigned int) specifies the
              error  to  be  returned  when a search hits this key; typically,
              this is one of EKEYREJECTED, EKEYREVOKED, or EKEYEXPIRED.

              If arg5 (cast to key_serial_t) is nonzero, then, subject to  the
              same  constraints  and  rules  as  KEYCTL_LINK,  the  negatively
              instantiated key is linked into the keyring whose ID  is  speci-
              fied in arg5.

              The  caller  must  have  the  appropriate authorization key.  In
              other words, this operation is available only  from  a  request-
              key(8)-style program.  See request_key(2).

              The caller must have the appropriate authorization key, and once
              the uninstantiated key has been instantiated, the  authorization
              key  is  revoked.   In  other words, this operation is available
              only from a request-key(8)-style  program.   See  request_key(2)
              for an explanation of uninstantiated keys and key instantiation.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_reject(3).

       KEYCTL_INSTANTIATE_IOV (since Linux 2.6.39)
              Instantiate an uninstantiated key with a payload specified via a
              vector of buffers.

              This  operation  is the same as KEYCTL_INSTANTIATE, but the pay-
              load data is specified as an array of iovec structures:

                  struct iovec {
                      void  *iov_base;    /* Starting address of buffer */
                      size_t iov_len;     /* Size of buffer (in bytes) */
                  };

              The pointer to the payload vector is specified in arg3 (cast  as
              const  struct  iovec *).   The  number of items in the vector is
              specified in arg4 (cast as unsigned int).

              The arg2 (key ID) and arg5 (keyring ID) are interpreted  as  for
              KEYCTL_INSTANTIATE.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_instantiate_iov(3).

       KEYCTL_INVALIDATE (since Linux 3.5)
              Mark a key as invalid.

              The ID of the key to be invalidated is specified in  arg2  (cast
              to key_serial_t).

              To  invalidate  a key, the caller must have search permission on
              the key.

              This operation marks the key as invalid and schedules  immediate
              garbage  collection.   The garbage collector removes the invali-
              dated key from all keyrings and deletes the key when its  refer-
              ence  count reaches zero.  After this operation, the key will be
              ignored by all searches, even if it is not yet deleted.

              Keys that are marked invalid  become  invisible  to  normal  key
              operations   immediately,  though  they  are  still  visible  in
              /proc/keys (marked with an 'i' flag)  until  they  are  actually
              removed.

              The arguments arg3, arg4, and arg5 are ignored.

              This  operation  is  exposed  by  libkeyutils  via  the function
              keyctl_invalidate(3).

       KEYCTL_GET_PERSISTENT (since Linux 3.13)
              Get the persistent keyring (persistent-keyring(7)) for a  speci-
              fied user and link it to a specified keyring.

              The  user ID is specified in arg2 (cast to uid_t).  If the value
              -1 is specified, the caller's real user ID is used.  The  ID  of
              the   destination   keyring   is  specified  in  arg3  (cast  to
              key_serial_t).

              The caller must have  the  CAP_SETUID  capability  in  its  user
              namespace in order to fetch the persistent keyring for a user ID
              that does not match either the real or effective user ID of  the
              caller.

              If  the  call is successful, a link to the persistent keyring is
              added to the keyring whose ID was specified in arg3.

              The caller must have write permission on the keyring.

              The persistent keyring will be created by the kernel if it  does
              not yet exist.

              Each  time the KEYCTL_GET_PERSISTENT operation is performed, the
              persistent keyring will have its expiration timeout reset to the
              value in:

                  /proc/sys/kernel/keys/persistent_keyring_expiry

              Should  the  timeout  be reached, the persistent keyring will be
              removed and everything it pins can then be garbage collected.

              Persistent keyrings were added to Linux in kernel version 3.13.

              The arguments arg4 and arg5 are ignored.

              This operation  is  exposed  by  libkeyutils  via  the  function
              keyctl_get_persistent(3).

       KEYCTL_DH_COMPUTE (since Linux 4.7)
              Compute a Diffie-Hellman shared secret or public key, optionally
              applying key derivation function (KDF) to the result.

              The arg2 argument is a pointer to a set of parameters containing
              serial  numbers for three "user" keys used in the Diffie-Hellman
              calculation, packaged in a structure of the following form:

                  struct keyctl_dh_params {
                      int32_t private; /* The local private key */
                      int32_t prime; /* The prime, known to both parties */
                      int32_t base;  /* The base integer: either a shared
                                        generator or the remote public key */
                  };

              Each of the three keys specified in this  structure  must  grant
              the caller read permission.  The payloads of these keys are used
              to calculate the Diffie-Hellman result as:

                  base ^ private mod prime

              If the base is the shared generator, the  result  is  the  local
              public key.  If the base is the remote public key, the result is
              the shared secret.

              The arg3 argument (cast to char *) points to a buffer where  the
              result of the calculation is placed.  The size of that buffer is
              specified in arg4 (cast to size_t).

              The buffer must be large enough to accommodate the output  data,
              otherwise  an  error is returned.  If arg4 is specified zero, in
              which case the buffer is not used and the operation returns  the
              minimum required buffer size (i.e., the length of the prime).

              Diffie-Hellman  computations can be performed in user space, but
              require a multiple-precision integer (MPI) library.  Moving  the
              implementation  into  the  kernel gives access to the kernel MPI
              implementation, and allows  access  to  secure  or  acceleration
              hardware.

              Adding  support  for  DH computation to the keyctl() system call
              was considered a good fit due to  the  DH  algorithm's  use  for
              deriving  shared  keys;  it  also  allows the type of the key to
              determine which DH  implementation  (software  or  hardware)  is
              appropriate.

              If  the  arg5  argument  is  NULL,  then the DH result itself is
              returned.  Otherwise (since Linux 4.12), it is a  pointer  to  a
              structure  which specifies parameters of the KDF operation to be
              applied:

                  struct keyctl_kdf_params {
                      char *hashname;     /* Hash algorithm name */
                      char *otherinfo;    /* SP800-56A OtherInfo */
                      __u32 otherinfolen; /* Length of otherinfo data */
                      __u32 __spare[8];   /* Reserved */
                  };

              The hashname field is a null-terminated string which specifies a
              hash name (available in the kernel's crypto API; the list of the
              hashes available is rather tricky to observe;  please  refer  to
              the "Kernel Crypto API Architecture" <https://www.kernel.org/doc
              /html/latest/crypto/architecture.html>  documentation  for   the
              information  regarding  how  hash names are constructed and your
              kernel's source and configuration  regarding  what  ciphers  and
              templates  with  type CRYPTO_ALG_TYPE_SHASH are available) to be
              applied to DH result in KDF operation.

              The otherinfo  field  is  an  OtherInfo  data  as  described  in
              SP800-56A  section 5.8.1.2 and is algorithm-specific.  This data
              is concatenated with the result of DH operation and is  provided
              as  an  input to the KDF operation.  Its size is provided in the
              otherinfolen field and is limited by KEYCTL_KDF_MAX_OI_LEN  con-
              stant that defined in security/keys/internal.h to a value of 64.

              The  __spare  field  is  currently unused.  It was ignored until
              Linux 4.13 (but still should be  user-addressable  since  it  is
              copied  to  the  kernel),  and should contain zeroes since Linux
              4.13.

              The KDF implementation complies with SP800-56A as well  as  with
              SP800-108 (the counter KDF).

              This  operation  is  exposed by libkeyutils (from version 1.5.10
              onwards)   via   the    functions    keyctl_dh_compute(3)    and
              keyctl_dh_compute_alloc(3).

       KEYCTL_RESTRICT_KEYRING (since Linux 4.12)
              Apply  a key-linking restriction to the keyring with the ID pro-
              vided in arg2 (cast to  key_serial_t).   The  caller  must  have
              setattr  permission on the key.  If arg3 is NULL, any attempt to
              add a key to the keyring is blocked;  otherwise  it  contains  a
              pointer  to  a  string  with a key type name and arg4 contains a
              pointer to string that describes the type-specific  restriction.
              As  of  Linux  4.12, only the type "asymmetric" has restrictions
              defined:

              builtin_trusted
                     Allows only keys that are signed by a key linked  to  the
                     builtin keyring (".builtin_trusted_keys").

              builtin_and_secondary_trusted
                     Allows  only  keys that are signed by a key linked to the
                     secondary  keyring  (".secondary_trusted_keys")  or,   by
                     extension,  a  key in a builtin keyring, as the latter is
                     linked to the former.

              key_or_keyring:key
              key_or_keyring:key:chain
                     If key specifies the ID of a key  of  type  "asymmetric",
                     then only keys that are signed by this key are allowed.

                     If key specifies the ID of a keyring, then only keys that
                     are signed by a key linked to this keyring are allowed.

                     If ":chain" is specified, keys that are signed by a  keys
                     linked  to  the destination keyring (that is, the keyring
                     with the ID specified in  the  arg2  argument)  are  also
                     allowed.

              Note  that  a  restriction  can  be configured only once for the
              specified keyring; once a restriction is set, it can't be  over-
              ridden.

              The argument arg5 is ignored.

RETURN VALUE
       For a successful call, the return value depends on the operation:

       KEYCTL_GET_KEYRING_ID
              The ID of the requested keyring.

       KEYCTL_JOIN_SESSION_KEYRING
              The ID of the joined session keyring.

       KEYCTL_DESCRIBE
              The  size  of  the  description  (including the terminating null
              byte), irrespective of the provided buffer size.

       KEYCTL_SEARCH
              The ID of the key that was found.

       KEYCTL_READ
              The amount of data that is available in the key, irrespective of
              the provided buffer size.

       KEYCTL_SET_REQKEY_KEYRING
              The  ID  of  the  previous  default  keyring to which implicitly
              requested keys were linked (one of KEY_REQKEY_DEFL_USER_*).

       KEYCTL_ASSUME_AUTHORITY
              Either 0, if the ID given was 0, or the ID of the  authorization
              key  matching  the  specified  key, if a nonzero key ID was pro-
              vided.

       KEYCTL_GET_SECURITY
              The size of the LSM security label string (including the  termi-
              nating null byte), irrespective of the provided buffer size.

       KEYCTL_GET_PERSISTENT
              The ID of the persistent keyring.

       KEYCTL_DH_COMPUTE
              The  number of bytes copied to the buffer, or, if arg4 is 0, the
              required buffer size.

       All other operations
              Zero.

       On error, -1 is returned, and errno is set  appropriately  to  indicate
       the error.

ERRORS
       EACCES The requested operation wasn't permitted.

       EAGAIN operation  was  KEYCTL_DH_COMPUTE  and there was an error during
              crypto module initialisation.

       EDEADLK
              operation was KEYCTL_LINK and the requested link would result in
              a cycle.

       EDEADLK
              operation  was KEYCTL_RESTRICT_KEYRING and the requested keyring
              restriction would result in a cycle.

       EDQUOT The key quota for the caller's user would be exceeded by  creat-
              ing a key or linking it to the keyring.

       EEXIST operation  was  KEYCTL_RESTRICT_KEYRING  and keyring provided in
              arg2 argument already has a restriction set.

       EFAULT operation was KEYCTL_DH_COMPUTE and one  of  the  following  has
              failed:

              o  copying  of the struct keyctl_dh_params, provided in the arg2
                 argument, from user space;

              o  copying of the struct keyctl_kdf_params, provided in the non-
                 NULL  arg5 argument, from user space (in case kernel supports
                 performing KDF operation on DH operation result);

              o  copying of data pointed by the hashname field of  the  struct
                 keyctl_kdf_params from user space;

              o  copying  of data pointed by the otherinfo field of the struct
                 keyctl_kdf_params from user space if the  otherinfolen  field
                 was nonzero;

              o  copying of the result to user space.

       EINVAL operation  was  KEYCTL_SETPERM and an invalid permission bit was
              specified in arg3.

       EINVAL operation was KEYCTL_SEARCH and the size of the  description  in
              arg4  (including the terminating null byte) exceeded 4096 bytes.
              size of the string (including the terminating null byte)  speci-
              fied  in  arg3  (the  key  type)  or  arg4 (the key description)
              exceeded the limit (32 bytes and 4096 bytes respectively).

       EINVAL (Linux kernels before 4.12)
              operation was KEYCTL_DH_COMPUTE, argument arg5 was non-NULL.

       EINVAL operation was KEYCTL_DH_COMPUTE And the digest size of the hash-
              ing algorithm supplied is zero.

       EINVAL operation  was KEYCTL_DH_COMPUTE and the buffer size provided is
              not enough to hold the result.  Provide 0 as a  buffer  size  in
              order to obtain the minimum buffer size.

       EINVAL operation  was  KEYCTL_DH_COMPUTE  and the hash name provided in
              the hashname field of the struct  keyctl_kdf_params  pointed  by
              arg5  argument  is too big (the limit is implementation-specific
              and varies between kernel versions, but it is deemed big  enough
              for all valid algorithm names).

       EINVAL operation  was  KEYCTL_DH_COMPUTE  and  the __spare field of the
              struct keyctl_kdf_params provided in the arg5 argument  contains
              nonzero values.

       EKEYEXPIRED
              An expired key was found or specified.

       EKEYREJECTED
              A rejected key was found or specified.

       EKEYREVOKED
              A revoked key was found or specified.

       ELOOP  operation was KEYCTL_LINK and the requested link would cause the
              maximum nesting depth for keyrings to be exceeded.

       EMSGSIZE
              operation was KEYCTL_DH_COMPUTE and the  buffer  length  exceeds
              KEYCTL_KDF_MAX_OUTPUT_LEN  (which is 1024 currently) or the oth-
              erinfolen field of the struct keyctl_kdf_parms  passed  in  arg5
              exceeds KEYCTL_KDF_MAX_OI_LEN (which is 64 currently).

       ENFILE (Linux kernels before 3.13)
              operation  was  KEYCTL_LINK  and  the  keyring is full.  (Before
              Linux 3.13, the available space for storing  keyring  links  was
              limited  to  a single page of memory; since Linux 3.13, there is
              no fixed limit.)

       ENOENT operation was KEYCTL_UNLINK and the key  to  be  unlinked  isn't
              linked to the keyring.

       ENOENT operation was KEYCTL_DH_COMPUTE and the hashing algorithm speci-
              fied in the  hashname  field  of  the  struct  keyctl_kdf_params
              pointed by arg5 argument hasn't been found.

       ENOENT operation  was  KEYCTL_RESTRICT_KEYRING and the type provided in
              arg3 argument doesn't support setting key linking restrictions.

       ENOKEY No matching key was found or an invalid key was specified.

       ENOKEY The value KEYCTL_GET_KEYRING_ID was specified in operation,  the
              key  specified in arg2 did not exist, and arg3 was zero (meaning
              don't create the key if it didn't exist).

       ENOMEM One of kernel memory allocation routines failed during the  exe-
              cution of the syscall.

       ENOTDIR
              A  key  of  keyring type was expected but the ID of a key with a
              different type was provided.

       EOPNOTSUPP
              operation was KEYCTL_READ and the  key  type  does  not  support
              reading (e.g., the type is "login").

       EOPNOTSUPP
              operation  was  KEYCTL_UPDATE  and the key type does not support
              updating.

       EOPNOTSUPP
              operation was KEYCTL_RESTRICT_KEYRING, the type provided in arg3
              argument was "asymmetric", and the key specified in the restric-
              tion specification provided in arg4 has type other  than  "asym-
              metric" or "keyring".

       EPERM  operation  was KEYCTL_GET_PERSISTENT, arg2 specified a UID other
              than the calling thread's real or effective UID, and the  caller
              did not have the CAP_SETUID capability.

       EPERM  operation  was  KEYCTL_SESSION_TO_PARENT  and either: all of the
              UIDs (GIDs) of the parent process do not match the effective UID
              (GID)  of  the calling process; the UID of the parent's existing
              session keyring or the UID of the caller's session  keyring  did
              not match the effective UID of the caller; the parent process is
              not single-thread; or the parent process is init(1) or a  kernel
              thread.

       ETIMEDOUT
              operation was KEYCTL_DH_COMPUTE and the initialisation of crypto
              modules has timed out.

VERSIONS
       This system call first appeared in Linux 2.6.10.

CONFORMING TO
       This system call is a nonstandard Linux extension.

NOTES
       No wrapper for this system call is provided in  glibc.   A  wrapper  is
       provided  in  the  libkeyutils  library.  When employing the wrapper in
       that library, link with -lkeyutils.  However, rather  than  using  this
       system  call  directly,  you  probably  want to use the various library
       functions mentioned in the descriptions of individual operations above.

EXAMPLE
       The program below provide subset of the functionality of  the  request-
       key(8)  program  provided  by  the keyutils package.  For informational
       purposes, the program records various information in a log file.

       As described in request_key(2), the request-key(8) program  is  invoked
       with command-line arguments that describe a key that is to be instanti-
       ated.  The example program fetches and logs these arguments.  The  pro-
       gram  assumes  authority  to  instantiate  the  requested key, and then
       instantiates that key.

       The following shell session demonstrates the use of this  program.   In
       the  session,  we  compile  the  program and then use it to temporarily
       replace the standard request-key(8) program.   (Note  that  temporarily
       disabling  the  standard request-key(8) program may not be safe on some
       systems.)  While our example program is installed, we use  the  example
       program shown in request_key(2) to request a key.

           $ cc -o key_instantiate key_instantiate.c -lkeyutils
           $ sudo mv /sbin/request-key /sbin/request-key.backup
           $ sudo cp key_instantiate /sbin/request-key
           $ ./t_request_key user mykey somepayloaddata
           Key ID is 20d035bf
           $ sudo mv /sbin/request-key.backup /sbin/request-key

       Looking  at  the  log file created by this program, we can see the com-
       mand-line arguments supplied to our example program:

           $ cat /tmp/key_instantiate.log
           Time: Mon Nov  7 13:06:47 2016

           Command line arguments:
             argv[0]:            /sbin/request-key
             operation:          create
             key_to_instantiate: 20d035bf
             UID:                1000
             GID:                1000
             thread_keyring:     0
             process_keyring:    0
             session_keyring:    256e6a6

           Key description:      user;1000;1000;3f010000;mykey
           Auth key payload:     somepayloaddata
           Destination keyring:  256e6a6
           Auth key description: .request_key_auth;1000;1000;0b010000;20d035bf

       The last few lines of the above output show that  the  example  program
       was able to fetch:

       *  the  description  of  the key to be instantiated, which included the
          name of the key (mykey);

       *  the payload of the authorization key, which consisted  of  the  data
          (somepayloaddata) passed to request_key(2);

       *  the   destination   keyring  that  was  specified  in  the  call  to
          request_key(2); and

       *  the description of the authorization key, where we can see that  the
          name  of  the authorization key matches the ID of the key that is to
          be instantiated (20d035bf).

       The example program in request_key(2) specified the destination keyring
       as  KEY_SPEC_SESSION_KEYRING.  By examining the contents of /proc/keys,
       we can see that this was  translated  to  the  ID  of  the  destination
       keyring  (0256e6a6)  shown in the log output above; we can also see the
       newly created key with the name mykey and ID 20d035bf.

           $ cat /proc/keys | egrep 'mykey|256e6a6'
           0256e6a6 I--Q---  194 perm 3f030000  1000  1000 keyring  _ses: 3
           20d035bf I--Q---    1 perm 3f010000  1000  1000 user     mykey: 16

   Program source

       /* key_instantiate.c */

       #include <sys/types.h>
       #include <keyutils.h>
       #include <time.h>
       #include <fcntl.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <string.h>
       #include <errno.h>

       #ifndef KEY_SPEC_REQUESTOR_KEYRING
       #define KEY_SPEC_REQUESTOR_KEYRING      -8
       #endif

       int
       main(int argc, char *argv[])
       {
           FILE *fp;
           time_t t;
           char *operation;
           key_serial_t key_to_instantiate, dest_keyring;
           key_serial_t thread_keyring, process_keyring, session_keyring;
           uid_t uid;
           gid_t gid;
           char dbuf[256];
           char auth_key_payload[256];
           int akp_size;       /* Size of auth_key_payload */

           fp = fopen("/tmp/key_instantiate.log", "w");
           if (fp == NULL)
               exit(EXIT_FAILURE);

           setbuf(fp, NULL);

           t = time(NULL);
           fprintf(fp, "Time: %s\n", ctime(&t));

           /*
            * The kernel passes a fixed set of arguments to the program
            * that it execs; fetch them.
            */
           operation = argv[1];
           key_to_instantiate = atoi(argv[2]);
           uid = atoi(argv[3]);
           gid = atoi(argv[4]);
           thread_keyring = atoi(argv[5]);
           process_keyring = atoi(argv[6]);
           session_keyring = atoi(argv[7]);

           fprintf(fp, "Command line arguments:\n");
           fprintf(fp, "  argv[0]:            %s\n", argv[0]);
           fprintf(fp, "  operation:          %s\n", operation);
           fprintf(fp, "  key_to_instantiate: %lx\n",
                   (long) key_to_instantiate);
           fprintf(fp, "  UID:                %ld\n", (long) uid);
           fprintf(fp, "  GID:                %ld\n", (long) gid);
           fprintf(fp, "  thread_keyring:     %lx\n", (long) thread_keyring);
           fprintf(fp, "  process_keyring:    %lx\n", (long) process_keyring);
           fprintf(fp, "  session_keyring:    %lx\n", (long) session_keyring);
           fprintf(fp, "\n");

           /*
            * Assume the authority to instantiate the key named in argv[2]
            */
           if (keyctl(KEYCTL_ASSUME_AUTHORITY, key_to_instantiate) == -1) {
               fprintf(fp, "KEYCTL_ASSUME_AUTHORITY failed: %s\n",
                       strerror(errno));
               exit(EXIT_FAILURE);
           }

           /*
            * Fetch the description of the key that is to be instantiated
            */
           if (keyctl(KEYCTL_DESCRIBE, key_to_instantiate,
                       dbuf, sizeof(dbuf)) == -1) {
               fprintf(fp, "KEYCTL_DESCRIBE failed: %s\n", strerror(errno));
               exit(EXIT_FAILURE);
           }

           fprintf(fp, "Key description:      %s\n", dbuf);

           /*
            * Fetch the payload of the authorization key, which is
            * actually the callout data given to request_key()
            */
           akp_size = keyctl(KEYCTL_READ, KEY_SPEC_REQKEY_AUTH_KEY,
                             auth_key_payload, sizeof(auth_key_payload));
           if (akp_size == -1) {
               fprintf(fp, "KEYCTL_READ failed: %s\n", strerror(errno));
               exit(EXIT_FAILURE);
           }

           auth_key_payload[akp_size] = '\0';
           fprintf(fp, "Auth key payload:     %s\n", auth_key_payload);

           /*
            * For interest, get the ID of the authorization key and
            * display it.
            */
           auth_key = keyctl(KEYCTL_GET_KEYRING_ID,
                   KEY_SPEC_REQKEY_AUTH_KEY);
           if (auth_key == -1) {
               fprintf(fp, "KEYCTL_GET_KEYRING_ID failed: %s\n",
                       strerror(errno));
               exit(EXIT_FAILURE);
           }

           fprintf(fp, "Auth key ID:          %lx\n", (long) auth_key);

           /*
            * Fetch key ID for the request_key(2) destination keyring.
            */
           dest_keyring = keyctl(KEYCTL_GET_KEYRING_ID,
                                 KEY_SPEC_REQUESTOR_KEYRING);
           if (dest_keyring == -1) {
               fprintf(fp, "KEYCTL_GET_KEYRING_ID failed: %s\n",
                       strerror(errno));
               exit(EXIT_FAILURE);
           }

           fprintf(fp, "Destination keyring:  %lx\n", (long) dest_keyring);

           /*
            * Fetch the description of the authorization key. This
            * allows us to see the key type, UID, GID, permissions,
            * and description (name) of the key. Among other things,
            * we will see that the name of the key is a hexadecimal
            * string representing the ID of the key to be instantiated.
            */
           if (keyctl(KEYCTL_DESCRIBE, KEY_SPEC_REQKEY_AUTH_KEY,
                       dbuf, sizeof(dbuf)) == -1) {
               fprintf(fp, "KEYCTL_DESCRIBE failed: %s\n", strerror(errno));
               exit(EXIT_FAILURE);
           }

           fprintf(fp, "Auth key description: %s\n", dbuf);

           /*
            * Instantiate the key using the callout data that was supplied
            * in the payload of the authorization key.
            */
           if (keyctl(KEYCTL_INSTANTIATE, key_to_instantiate,
                      auth_key_payload, akp_size + 1, dest_keyring) == -1) {
               fprintf(fp, "KEYCTL_INSTANTIATE failed: %s\n",
                       strerror(errno));
               exit(EXIT_FAILURE);
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       keyctl(1), add_key(2), request_key(2), keyctl(3),
       keyctl_assume_authority(3), keyctl_chown(3), keyctl_clear(3),
       keyctl_describe(3), keyctl_describe_alloc(3), keyctl_dh_compute(3),
       keyctl_dh_compute_alloc(3), keyctl_get_keyring_ID(3),
       keyctl_get_persistent(3), keyctl_get_security(3),
       keyctl_get_security_alloc(3), keyctl_instantiate(3),
       keyctl_instantiate_iov(3), keyctl_invalidate(3),
       keyctl_join_session_keyring(3), keyctl_link(3), keyctl_negate(3),
       keyctl_read(3), keyctl_read_alloc(3), keyctl_reject(3),
       keyctl_revoke(3), keyctl_search(3), keyctl_session_to_parent(3),
       keyctl_set_reqkey_keyring(3), keyctl_set_timeout(3), keyctl_setperm(3),
       keyctl_unlink(3), keyctl_update(3), recursive_key_scan(3),
       recursive_session_key_scan(3), capabilities(7), credentials(7),
       keyrings(7), keyutils(7), persistent-keyring(7), process-keyring(7),
       session-keyring(7), thread-keyring(7), user-keyring(7),
       user_namespaces(7), user-session-keyring(7), request-key(8)

       The kernel source files under Documentation/security/keys/ (or, before
       Linux 4.13, in the file Documentation/security/keys.txt).

COLOPHON
       This page is part of release 4.15 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                             2017-09-15                         KEYCTL(2)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2021 Hurricane Electric. All Rights Reserved.