man2/add_key.2

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   2 .\"     Written by David Howells (dhowells@redhat.com)
   3 .\" and Copyright (C) 2016 Michael Kerrisk <mtk.man-pages@gmail.com>
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  11 .\"
  12 .TH ADD_KEY 2 2020-11-01 Linux "Linux Key Management Calls"
  13 .SH NAME
  14 add_key \- add a key to the kernel's key management facility
  15 .SH SYNOPSIS
  16 .nf
  17 .B #include <sys/types.h>
  18 .B #include <keyutils.h>
  19 .PP
  20 .BI "key_serial_t add_key(const char *" type ", const char *" description ,
  21 .BI "                     const void *" payload ", size_t " plen ,
  22 .BI "                     key_serial_t " keyring ");"
  23 .fi
  24 .PP
  25 .IR Note :
  26 There is no glibc wrapper for this system call; see NOTES.
  27 .SH DESCRIPTION
  28 .BR add_key ()
  29 creates or updates a key of the given
  30 .I type
  31 and
  32 .IR description ,
  33 instantiates it with the
  34 .I payload
  35 of length
  36 .IR plen ,
  37 attaches it to the nominated
  38 .IR keyring ,
  39 and returns the key's serial number.
  40 .PP
  41 The key may be rejected if the provided data is in the wrong format or
  42 it is invalid in some other way.
  43 .PP
  44 If the destination
  45 .I keyring
  46 already contains a key that matches the specified
  47 .IR type
  48 and
  49 .IR description ,
  50 then, if the key type supports it,
  51 .\" FIXME The aforementioned phrases begs the question:
  52 .\" which key types support this?
  53 that key will be updated rather than a new key being created;
  54 if not, a new key (with a different ID) will be created
  55 and it will displace the link to the extant key from the keyring.
  56 .\" FIXME Perhaps elaborate the implications here? Namely, the new
  57 .\" key will have a new ID, and if the old key was a keyring that
  58 .\" is consequently unlinked, then keys that it was anchoring
  59 .\" will have their reference count decreased by one (and may
  60 .\" consequently be garbage collected). Is this all correct?
  61 .PP
  62 The destination
  63 .I keyring
  64 serial number may be that of a valid keyring for which the caller has
  65 .I write
  66 permission.
  67 Alternatively, it may be one of the following special keyring IDs:
  68 .\" FIXME . Perhaps have a separate page describing special keyring IDs?
  69 .TP
  70 .B KEY_SPEC_THREAD_KEYRING
  71 This specifies the caller's thread-specific keyring
  72 .RB ( thread-keyring (7)).
  73 .TP
  74 .B KEY_SPEC_PROCESS_KEYRING
  75 This specifies the caller's process-specific keyring
  76 .RB ( process-keyring (7)).
  77 .TP
  78 .B KEY_SPEC_SESSION_KEYRING
  79 This specifies the caller's session-specific keyring
  80 .RB ( session-keyring (7)).
  81 .TP
  82 .B KEY_SPEC_USER_KEYRING
  83 This specifies the caller's UID-specific keyring
  84 .RB ( user-keyring (7)).
  85 .TP
  86 .B KEY_SPEC_USER_SESSION_KEYRING
  87 This specifies the caller's UID-session keyring
  88 .RB ( user-session-keyring (7)).
  89 .SS Key types
  90 The key
  91 .I type
  92 is a string that specifies the key's type.
  93 Internally, the kernel defines a number of key types that are
  94 available in the core key management code.
  95 Among the types that are available for user-space use
  96 and can be specified as the
  97 .I type
  98 argument to
  99 .BR add_key ()
 100 are the following:
 101 .TP
 102 .I """keyring"""
 103 Keyrings are special key types that may contain links to sequences of other
 104 keys of any type.
 105 If this interface is used to create a keyring, then
 106 .I payload
 107 should be NULL and
 108 .I plen
 109 should be zero.
 110 .TP
 111 .IR """user"""
 112 This is a general purpose key type whose payload may be read and updated
 113 by user-space applications.
 114 The key is kept entirely within kernel memory.
 115 The payload for keys of this type is a blob of arbitrary data
 116 of up to 32,767 bytes.
 117 .TP
 118 .IR """logon""" " (since Linux 3.3)"
 119 .\" commit 9f6ed2ca257fa8650b876377833e6f14e272848b
 120 This key type is essentially the same as
 121 .IR """user""" ,
 122 but it does not permit the key to read.
 123 This is suitable for storing payloads
 124 that you do not want to be readable from user space.
 125 .PP
 126 This key type vets the
 127 .I description
 128 to ensure that it is qualified by a "service" prefix,
 129 by checking to ensure that the
 130 .I description
 131 contains a ':' that is preceded by other characters.
 132 .TP
 133 .IR """big_key""" " (since Linux 3.13)"
 134 .\" commit ab3c3587f8cda9083209a61dbe3a4407d3cada10
 135 This key type is similar to
 136 .IR """user""" ,
 137 but may hold a payload of up to 1\ MiB.
 138 If the key payload is large enough,
 139 then it may be stored encrypted in tmpfs
 140 (which can be swapped out) rather than kernel memory.
 141 .PP
 142 For further details on these key types, see
 143 .BR keyrings (7).
 144 .SH RETURN VALUE
 145 On success,
 146 .BR add_key ()
 147 returns the serial number of the key it created or updated.
 148 On error, \-1 is returned and
 149 .I errno
 150 is set to indicate the cause of the error.
 151 .SH ERRORS
 152 .TP
 153 .B EACCES
 154 The keyring wasn't available for modification by the user.
 155 .TP
 156 .B EDQUOT
 157 The key quota for this user would be exceeded by creating this key or linking
 158 it to the keyring.
 159 .TP
 160 .B EFAULT
 161 One or more of
 162 .IR type ,
 163 .IR description ,
 164 and
 165 .I payload
 166 points outside process's accessible address space.
 167 .TP
 168 .B EINVAL
 169 The size of the string (including the terminating null byte) specified in
 170 .I type
 171 or
 172 .I description
 173 exceeded the limit (32 bytes and 4096 bytes respectively).
 174 .TP
 175 .B EINVAL
 176 The payload data was invalid.
 177 .TP
 178 .B EINVAL
 179 .IR type
 180 was
 181 .IR """logon"""
 182 and the
 183 .I description
 184 was not qualified with a prefix string of the form
 185 .IR """service:""" .
 186 .TP
 187 .B EKEYEXPIRED
 188 The keyring has expired.
 189 .TP
 190 .B EKEYREVOKED
 191 The keyring has been revoked.
 192 .TP
 193 .B ENOKEY
 194 The keyring doesn't exist.
 195 .TP
 196 .B ENOMEM
 197 Insufficient memory to create a key.
 198 .TP
 199 .B EPERM
 200 The
 201 .I type
 202 started with a period (\(aq.\(aq).
 203 Key types that begin with a period are reserved to the implementation.
 204 .TP
 205 .B EPERM
 206 .I type
 207 was
 208 .I """keyring"""
 209 and the
 210 .I description
 211 started with a period (\(aq.\(aq).
 212 Keyrings with descriptions (names)
 213 that begin with a period are reserved to the implementation.
 214 .SH VERSIONS
 215 This system call first appeared in Linux 2.6.10.
 216 .SH CONFORMING TO
 217 This system call is a nonstandard Linux extension.
 218 .SH NOTES
 219 Glibc does not provide a wrapper for this system call.
 220 A wrapper is provided in the
 221 .IR libkeyutils
 222 package.
 223 When employing the wrapper in that library, link with
 224 .IR \-lkeyutils .
 225 .SH EXAMPLES
 226 The program below creates a key with the type, description, and payload
 227 specified in its command-line arguments,
 228 and links that key into the session keyring.
 229 The following shell session demonstrates the use of the program:
 230 .PP
 231 .in +4n
 232 .EX
 233 $ \fB./a.out user mykey "Some payload"\fP
 234 Key ID is 64a4dca
 235 $ \fBgrep \(aq64a4dca\(aq /proc/keys\fP
 236 064a4dca I--Q---    1 perm 3f010000  1000  1000 user    mykey: 12
 237 .EE
 238 .in
 239 .SS Program source
 240 \&
 241 .EX
 242 #include <sys/types.h>
 243 #include <keyutils.h>
 244 #include <stdint.h>
 245 #include <stdio.h>
 246 #include <stdlib.h>
 247 #include <string.h>
 248
 249 int
 250 main(int argc, char *argv[])
 251 {
 252     key_serial_t key;
 253
 254     if (argc != 4) {
 255         fprintf(stderr, "Usage: %s type description payload\en",
 256                 argv[0]);
 257         exit(EXIT_FAILURE);
 258     }
 259
 260     key = add_key(argv[1], argv[2], argv[3], strlen(argv[3]),
 261                 KEY_SPEC_SESSION_KEYRING);
 262     if (key == \-1) {
 263         perror("add_key");
 264         exit(EXIT_FAILURE);
 265     }
 266
 267     printf("Key ID is %jx\en", (uintmax_t) key);
 268
 269     exit(EXIT_SUCCESS);
 270 }
 271 .EE
 272 .SH SEE ALSO
 273 .ad l
 274 .nh
 275 .BR keyctl (1),
 276 .BR keyctl (2),
 277 .BR request_key (2),
 278 .BR keyctl (3),
 279 .BR keyrings (7),
 280 .BR keyutils (7),
 281 .BR persistent\-keyring (7),
 282 .BR process\-keyring (7),
 283 .BR session\-keyring (7),
 284 .BR thread\-keyring (7),
 285 .BR user\-keyring (7),
 286 .BR user\-session\-keyring (7)
 287 .PP
 288 The kernel source files
 289 .IR Documentation/security/keys/core.rst
 290 and
 291 .IR Documentation/keys/request\-key.rst
 292 (or, before Linux 4.13, in the files
 293 .\" commit b68101a1e8f0263dbc7b8375d2a7c57c6216fb76
 294 .IR Documentation/security/keys.txt
 295 and
 296 .\" commit 3db38ed76890565772fcca3279cc8d454ea6176b
 297 .IR Documentation/security/keys\-request\-key.txt ).