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       request_key - Request a key from the kernel’s key management facility


       #include <keyutils.h>

       key_serial_t request_key(const char *type, const char *description,
       const char *callout_info, key_serial_t keyring);


       request_key()  asks  the  kernel  to  find a key of the given type that
       matches the specified description and, if successful, to attach  it  to
       the nominated keyring and to return its serial number.

       request_key()  first  recursively searches all the keyrings attached to
       the calling process in  the  order  thread-specific  keyring,  process-
       specific keyring and then session keyring for a matching key.

       If  request_key()  is called from a program invoked by request_key() on
       behalf of some other process to generate a key, then  the  keyrings  of
       that  other  process  will be searched next, using that other process’s
       UID, GID, groups and security context to control access.

       The keys in each keyring searched are checked for a  match  before  any
       child  keyrings  are  recursed into.  Only keys that are searchable for
       the caller may be found, and only searchable keyrings may be  searched.

       If  the  key  is  not found then, if callout_info is set, this function
       will attempt to look further afield.  In such a case, the  callout_info
       is  passed to a userspace service such as /sbin/request-key to generate
       the key.

       If that is unsuccessful also, then an error will  be  returned,  and  a
       temporary  negative  key  will  be  installed in the nominated keyring.
       This will expire after a few seconds, but will cause  subsequent  calls
       to request_key() to fail until it does.

       The  keyring  serial number may be that of a valid keyring to which the
       caller has write permission, or it may be a special keyring ID:

              This specifies the caller’s thread-specific keyring.

              This specifies the caller’s process-specific keyring.

              This specifies the caller’s session-specific keyring.

              This specifies the caller’s UID-specific keyring.

              This specifies the caller’s UID-session keyring.

       If a key is created, no matter whether it’s a valid key or  a  negative
       key,  it  will  displace any other key of the same type and description
       from the destination keyring.


       On success request_key() returns the serial number of the key it found.
       On error, the value -1 will be returned and errno will have been set to
       an appropriate error.


       ENOKEY No matching key was found.

              An expired key was found, but no replacement could be  obtained.

              A revoked key was found, but no replacement could be obtained.

              The attempt to generate a new key was rejected.

       ENOMEM Insufficient memory to create a key.

       EINTR  The request was interrupted by a signal.

       EDQUOT The  key  quota for this user would be exceeded by creating this
              key or linking it to the keyring.

       EACCES The keyring wasn’t available for modification by the user.


       Although this is a Linux system call, it is not present in libc but can
       be  found  rather  in  libkeyutils.  When linking, -lkeyutils should be
       specified to the linker.


       keyctl(1), add_key(2), keyctl(2), request-key(8)


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