man-pages/man2/add_key.2

.\" Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
.\"     Written by David Howells (dhowells@redhat.com)
.\" and Copyright (C) 2016 Michael Kerrisk <mtk.man-pages@gmail.com>
.\"
.\" %%%LICENSE_START(GPLv2+_SW_ONEPARA)
.\" This program is free software; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License
.\" as published by the Free Software Foundation; either version
.\" 2 of the License, or (at your option) any later version.
.\" %%%LICENSE_END
.\"
.TH ADD_KEY 2 2016-07-17 Linux "Linux Key Management Calls"
.SH NAME
add_key \- add a key to the kernel's key management facility
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <keyutils.h>
.sp
.BI "key_serial_t add_key(const char *" type ", const char *" description ,
.BI "                     const void *" payload ", size_t " plen ,
.BI "                     key_serial_t " keyring ");"
.fi

No glibc wrapper is provided for this system call; see NOTES.
.SH DESCRIPTION
.BR add_key ()
creates or updates a key of the given
.I type
and
.IR description ,
instantiates it with the
.I payload
of length
.IR plen ,
attaches it to the nominated
.IR keyring ,
and return the key's serial number.
.P
The key type may reject the data if it is in the wrong format or
is in some other way invalid.
.P
If the destination
.I keyring
already contains a key that matches the specified
.IR type
and
.IR 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.
.P
The destination
.I keyring
serial number may be that of a valid keyring for which the caller has
.I write
permission, or it may be one of the following special keyring IDs:
.\" FIXME Perhaps have a separate page describing special keyring IDs?
.TP
.B KEY_SPEC_THREAD_KEYRING
This specifies the caller's thread-specific keyring
.RB ( thread-keyring (7)).
.TP
.B KEY_SPEC_PROCESS_KEYRING
This specifies the caller's process-specific keyring
.RB ( process-keyring (7)).
.TP
.B KEY_SPEC_SESSION_KEYRING
This specifies the caller's session-specific keyring
.RB ( session-keyring (7)).
.TP
.B KEY_SPEC_USER_KEYRING
This specifies the caller's UID-specific keyring
.RB ( user-keyring (7)).
.TP
.B KEY_SPEC_USER_SESSION_KEYRING
This specifies the caller's UID-session keyring
.RB ( user-session-keyring (7)).
.SS Key types
The key
.I 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.
The following types are available for user-space use,
and can be specified as the
.I type
argument to
.BR add_key ():
.TP
.IR """user"""
The payload for keys of this type is a blob of arbitrary data
of up to 32,767 bytes.
The
.I description
may be any valid string, though it is preferred that it
start with a colon-delimited prefix representing the service
to which the key is of interest
(for instance
.IR """afs:mykey""" ).
.TP
.I """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 a NULL
.I payload
should be specified, and
.I plen
should be zero.
.TP
.IR """logon""" " (since Linux 3.3)"
.\" commit 9f6ed2ca257fa8650b876377833e6f14e272848b
This key type is essentially the same as
.IR """user""" ,
but does not provide reading (i.e., the
.BR keyctl (2)
.BR KEYCTL_READ
operation),
meaning that the key payload is never visible from user space.
This is suitable for storing username and password pairs in the keyring
that you do not want to be readable from user space.

This key type also vets the
.I description
to ensure that it is qualified by a "service" prefix,
by checking to ensure that the
.I description
contains a ':' that is preceded by other characters.
.TP
.IR """big_key""" " (since Linux 3.13)"
.\" commit ab3c3587f8cda9083209a61dbe3a4407d3cada10
This key type is similar to
.IR """user""" ,
but may hold a payload of up to 1 MiB.
For this key type,
the contents can be saved in a tmpfs filesystem and
thus swapped out to disk when memory pressure is high.
This key type is useful for tasks such as holding Kerberos ticket caches.
.\" David Howells: there are also other key types available for
.\" user-space use.
.SH RETURN VALUE
On success,
.BR add_key ()
returns the serial number of the key it created or updated.
On error, \-1 is returned and
.I errno
is set to indicate the cause of the error.
.SH ERRORS
.TP
.B EACCES
The keyring wasn't available for modification by the user.
.TP
.B EDQUOT
The key quota for this user would be exceeded by creating this key or linking
it to the keyring.
.TP
.B EINVAL
The size of the string (including the terminating null byte) specified in
.I type
or
.I description
exceeded the limit (32 bytes and 4096 bytes respectively).
.TP
.B EINVAL
The payload data was invalid.
.TP
.B EINVAL
.IR type
was
.IR """logon"""
and the
.I description
was not qualified with a prefix string of the form
.IR """service:""" .
.TP
.B EKEYEXPIRED
The keyring has expired.
.TP
.B EKEYREVOKED
The keyring has been revoked.
.TP
.B ENOKEY
The keyring doesn't exist.
.TP
.B ENOMEM
Insufficient memory to create a key.
.SH VERSIONS
This system call first appeared in Linux 2.6.11.
.SH CONFORMING TO
This system call is a nonstandard Linux extension.
.SH NOTES
No wrapper for this system call is provided in glibc.
A wrapper is provided in the
.IR libkeyutils
package.
When employing the wrapper in that library, link with
.IR \-lkeyutils .
.SH 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:

.in +4n
.nf
$ \fB./a.out user mykey "Some payload"\fP
Key ID is 64a4dca
$ \fBgrep \(aq64a4dca\(aq /proc/keys\fP
064a4dca I--Q---    1 perm 3f010000  1000  1000 user    mykey: 12
.fi
.in
.SS Program source
\&
.nf
#include <sys/types.h>
#include <keyutils.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
                        } while (0)

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)
        errExit("add_key");

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

    exit(EXIT_SUCCESS);
}
.fi
.SH SEE ALSO
.ad l
.nh
.BR keyctl (1),
.BR keyctl (2),
.BR request_key (2),
.BR keyctl (3),
.BR keyutils (7),
.BR keyrings (7),
.BR persistent\-keyring (7),
.BR process\-keyring (7),
.BR session\-keyring (7),
.BR thread\-keyring (7),
.BR user\-keyring (7),
.BR user\-session\-keyring (7)

The kernel source files
.IR Documentation/security/keys.txt
and
.IR Documentation/security/keys\-request\-key.txt .