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

NAME

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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <keyutils.h>

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

       Note: There is no glibc wrapper 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 following:

"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 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.

STANDARDS

       This system call is a nonstandard Linux extension.

NOTES

       glibc does not provide a wrapper for this system call.   A  wrapper  is  provided  in  the
       libkeyutils  library.   (The  accompanying package provides the <keyutils.h> header file.)
       When employing the wrapper in that library, link with -lkeyutils.

EXAMPLES

       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 <keyutils.h>
       #include <stdint.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 %jx\n", (uintmax_t) key);

           exit(EXIT_SUCCESS);
       }