.\" 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>
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.TH add_key 2 2024-05-02 "Linux man-pages 6.8"
.SH NAME
add_key \- add a key to the kernel's key management facility
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <keyutils.h>
.P
.BI "key_serial_t add_key(const char *" type ", const char *" description ,
.BI "                     const void " payload [. plen "], size_t " plen ,
.BI "                     key_serial_t " keyring ");"
.fi
.P
.IR Note :
There is no glibc wrapper 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 returns the key's serial number.
.P
The key may be rejected if the provided data is in the wrong format or
it is invalid in some other way.
.P
If the destination
.I keyring
already contains a key that matches the specified
.I type
and
.IR description ,
then, if the key type supports it,
.\" FIXME The aforementioned phrases begs the question:
.\" which key types support this?
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.
.\" FIXME Perhaps elaborate the implications here? Namely, the new
.\" key will have a new ID, and if the old key was a keyring that
.\" is consequently unlinked, then keys that it was anchoring
.\" will have their reference count decreased by one (and may
.\" consequently be garbage collected). Is this all correct?
.P
The destination
.I keyring
serial number may be that of a valid keyring for which the caller has
.I write
permission.
Alternatively, 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.
Among the types that are available for user-space use
and can be specified as the
.I type
argument to
.BR add_key ()
are the following:
.TP
.I \[dq]keyring\[dq]
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
.I payload
should be NULL and
.I plen
should be zero.
.TP
.I \[dq]user\[dq]
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.
.TP
.IR \[dq]logon\[dq] " (since Linux 3.3)"
.\" commit 9f6ed2ca257fa8650b876377833e6f14e272848b
This key type is essentially the same as
.IR \[dq]user\[dq] ,
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.
.P
This key type 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 \[dq]big_key\[dq] " (since Linux 3.13)"
.\" commit ab3c3587f8cda9083209a61dbe3a4407d3cada10
This key type is similar to
.IR \[dq]user\[dq] ,
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.
.P
For further details on these key types, see
.BR keyrings (7).
.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 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 EFAULT
One or more of
.IR type ,
.IR description ,
and
.I payload
points outside process's accessible address space.
.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
.I type
was
.I \[dq]logon\[dq]
and the
.I description
was not qualified with a prefix string of the form
.IR \[dq]service:\[dq] .
.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.
.TP
.B EPERM
The
.I type
started with a period (\[aq].\[aq]).
Key types that begin with a period are reserved to the implementation.
.TP
.B EPERM
.I type
was
.I \[dq]keyring\[dq]
and the
.I description
started with a period (\[aq].\[aq]).
Keyrings with descriptions (names)
that begin with a period are reserved to the implementation.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.6.10.
.SH NOTES
glibc does not provide a wrapper for this system call.
A wrapper is provided in the
.I libkeyutils
library.
(The accompanying package provides the
.I <keyutils.h>
header file.)
When employing the wrapper in that library, link with
.IR \-lkeyutils .
.SH 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:
.P
.in +4n
.EX
$ \fB./a.out user mykey "Some payload"\fP
Key ID is 64a4dca
$ \fBgrep \[aq]64a4dca\[aq] /proc/keys\fP
064a4dca I\-\-Q\-\-\-    1 perm 3f010000  1000  1000 user    mykey: 12
.EE
.in
.SS Program source
\&
.\" SRC BEGIN (add_key.c)
.EX
#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\en",
                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\en", (uintmax_t) key);
\&
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.ad l
.nh
.BR keyctl (1),
.BR keyctl (2),
.BR request_key (2),
.BR keyctl (3),
.BR keyrings (7),
.BR keyutils (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)
.P
The kernel source files
.I Documentation/security/keys/core.rst
and
.I Documentation/keys/request\-key.rst
(or, before Linux 4.13, in the files
.\" commit b68101a1e8f0263dbc7b8375d2a7c57c6216fb76
.I Documentation/security/keys.txt
and
.\" commit 3db38ed76890565772fcca3279cc8d454ea6176b
.IR Documentation/security/keys\-request\-key.txt ).