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ADD_KEY(2) Linux Key Management Calls ADD_KEY(2)

NAME

     add_key - add a key to the kernel's key management facility

SYNOPSIS

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

     key_serial_t add_key(const char *type, const char *description,
                          const void *payload, size_t plen,
                          key_serial_t keyring);

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

DESCRIPTION

     add_key()  creates  or updates a key of the given type and description,
     instantiates it with the payload of length plen,  attaches  it  to  the
     nominated keyring, and returns the key's serial number.

     The  key may be rejected if the provided data is in the wrong format or
     it is invalid in some other way.

     If the destination keyring already contains  a  key  that  matches  the
     specified type and description, then, if the key type supports it, that
     key will be updated rather than a new key being created; if not, a  new
     key (with a different ID) will be created and it will displace the link
     to the extant key from the keyring.

     The destination keyring serial number may be that of  a  valid  keyring
     for  which  the  caller has write permission.  Alternatively, it may be
     one of the following special keyring IDs:

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

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

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

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

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

 Key types
     The  key  type  is a string that specifies the key's type.  Internally,
     the kernel defines a number of key types that are available in the core
     key management code.  Among the types that are available for user-space
     use and can be specified as the type argument to add_key() are the fol-
     lowing:

     "keyring"
            Keyrings  are  special  key  types  that  may  contain  links to
            sequences of other keys of any type.  If this interface is  used
            to create a keyring, then payload should be NULL and plen should
            be zero.

     "user" This is a general purpose key type whose payload may be read and
            updated  by  user-space  applications.  The key is kept entirely
            within kernel memory.  The payload for keys of this  type  is  a
            blob of arbitrary data of up to 32,767 bytes.

     "logon" (since Linux 3.3)
            This key type is essentially the same as "user", but it does not
            permit the key to read.  This is suitable for  storing  payloads
            that you do not want to be readable from user space.

     This  key type vets the description to ensure that it is qualified by a
     "service" prefix, by checking to ensure that the description contains a
     ':' that is preceded by other characters.

     "big_key" (since Linux 3.13)
            This key type is similar to "user", but may hold a payload of up
            to 1 MiB.  If the key payload is large enough, then  it  may  be
            stored encrypted in tmpfs (which can be swapped out) rather than
            kernel memory.

     For further details on these key types, see keyrings(7).

RETURN VALUE

     On success, add_key() returns the serial number of the key  it  created
     or  updated.  On error, -1 is returned and errno is set to indicate the
     cause of the error.

ERRORS

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

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

     EFAULT One  or  more  of  type, description, and payload points outside
            process's accessible address space.

     EINVAL The size of the string (including  the  terminating  null  byte)
            specified  in  type  or description exceeded the limit (32 bytes
            and 4096 bytes respectively).

     EINVAL The payload data was invalid.

     EINVAL type was "logon" and the description was not  qualified  with  a
            prefix string of the form "service:".

     EKEYEXPIRED
            The keyring has expired.

     EKEYREVOKED
            The keyring has been revoked.

     ENOKEY The keyring doesn't exist.

     ENOMEM Insufficient memory to create a key.

     EPERM  The type started with a period ('.').  Key types that begin with
            a period are reserved to the implementation.

     EPERM  type was "keyring" and the description  started  with  a  period
            ('.').   Keyrings  with  descriptions  (names) that begin with a
            period are reserved to the implementation.

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  package.  When employing the wrapper in
     that library, link with -lkeyutils.

EXAMPLE

     The program below creates a key with the type, description, and payload
     specified  in  its  command-line arguments, and links that key into the
     session keyring.  The following shell session demonstrates the  use  of
     the program:

         $  ./a.out  user  mykey  "Some  payload"  Key  ID is 64a4dca $ grep
         '64a4dca' /proc/keys 064a4dca  I--Q---     1  perm  3f010000   1000
         1000 user    mykey: 12

 Program source
        #include  <sys/types.h>  #include  <keyutils.h>  #include  <stdio.h>
     #include <stdlib.h> #include <string.h>

     int main(int argc, char *argv[]) {
         key_serial_t key;

         if (argc != 4) {
             fprintf(stderr, "Usage: %s type description payload\n",
                     argv[0]);
             exit(EXIT_FAILURE);
         }

         key = add_key(argv[1], argv[2], argv[3], strlen(argv[3]),
                     KEY_SPEC_SESSION_KEYRING);
         if (key == -1) {
             perror("add_key");
             exit(EXIT_FAILURE);
         }

         printf("Key ID is %lx\n", (long) key);

         exit(EXIT_SUCCESS); }