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.

STANDARDS

       Linux.

HISTORY

       Linux 2.6.10.

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);
       }