The program below provide subset of the functionality of the
request-key(8) program provided by the keyutils package. For
informational purposes, the program records various information
in a log file.
As described in request_key(2), the request-key(8) program is
invoked with command-line arguments that describe a key that is
to be instantiated. The example program fetches and logs these
arguments. The program assumes authority to instantiate the
requested key, and then instantiates that key.
The following shell session demonstrates the use of this program.
In the session, we compile the program and then use it to
temporarily replace the standard request-key(8) program. (Note
that temporarily disabling the standard request-key(8) program
may not be safe on some systems.) While our example program is
installed, we use the example program shown in request_key(2) to
request a key.
$ cc -o key_instantiate key_instantiate.c -lkeyutils
$ sudo mv /sbin/request-key /sbin/request-key.backup
$ sudo cp key_instantiate /sbin/request-key
$ ./t_request_key user mykey somepayloaddata
Key ID is 20d035bf
$ sudo mv /sbin/request-key.backup /sbin/request-key
Looking at the log file created by this program, we can see the
command-line arguments supplied to our example program:
$ cat /tmp/key_instantiate.log
Time: Mon Nov 7 13:06:47 2016
Command line arguments:
argv[0]: /sbin/request-key
operation: create
key_to_instantiate: 20d035bf
UID: 1000
GID: 1000
thread_keyring: 0
process_keyring: 0
session_keyring: 256e6a6
Key description: user;1000;1000;3f010000;mykey
Auth key payload: somepayloaddata
Destination keyring: 256e6a6
Auth key description: .request_key_auth;1000;1000;0b010000;20d035bf
The last few lines of the above output show that the example
program was able to fetch:
* the description of the key to be instantiated, which included
the name of the key (mykey);
* the payload of the authorization key, which consisted of the
data (somepayloaddata) passed to request_key(2);
* the destination keyring that was specified in the call to
request_key(2); and
* the description of the authorization key, where we can see
that the name of the authorization key matches the ID of the
key that is to be instantiated (20d035bf).
The example program in request_key(2) specified the destination
keyring as KEY_SPEC_SESSION_KEYRING. By examining the contents
of /proc/keys, we can see that this was translated to the ID of
the destination keyring (0256e6a6) shown in the log output above;
we can also see the newly created key with the name mykey and ID
20d035bf.
$ cat /proc/keys | egrep 'mykey|256e6a6'
0256e6a6 I--Q--- 194 perm 3f030000 1000 1000 keyring _ses: 3
20d035bf I--Q--- 1 perm 3f010000 1000 1000 user mykey: 16
Program source
/* key_instantiate.c */
#include <sys/types.h>
#include <keyutils.h>
#include <time.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#ifndef KEY_SPEC_REQUESTOR_KEYRING
#define KEY_SPEC_REQUESTOR_KEYRING -8
#endif
int
main(int argc, char *argv[])
{
FILE *fp;
time_t t;
char *operation;
key_serial_t key_to_instantiate, dest_keyring;
key_serial_t thread_keyring, process_keyring, session_keyring;
uid_t uid;
gid_t gid;
char dbuf[256];
char auth_key_payload[256];
int akp_size; /* Size of auth_key_payload */
int auth_key;
fp = fopen("/tmp/key_instantiate.log", "w");
if (fp == NULL)
exit(EXIT_FAILURE);
setbuf(fp, NULL);
t = time(NULL);
fprintf(fp, "Time: %s\n", ctime(&t));
/*
* The kernel passes a fixed set of arguments to the program
* that it execs; fetch them.
*/
operation = argv[1];
key_to_instantiate = atoi(argv[2]);
uid = atoi(argv[3]);
gid = atoi(argv[4]);
thread_keyring = atoi(argv[5]);
process_keyring = atoi(argv[6]);
session_keyring = atoi(argv[7]);
fprintf(fp, "Command line arguments:\n");
fprintf(fp, " argv[0]: %s\n", argv[0]);
fprintf(fp, " operation: %s\n", operation);
fprintf(fp, " key_to_instantiate: %jx\n",
(uintmax_t) key_to_instantiate);
fprintf(fp, " UID: %jd\n", (intmax_t) uid);
fprintf(fp, " GID: %jd\n", (intmax_t) gid);
fprintf(fp, " thread_keyring: %jx\n",
(uintmax_t) thread_keyring);
fprintf(fp, " process_keyring: %jx\n",
(uintmax_t) process_keyring);
fprintf(fp, " session_keyring: %jx\n",
(uintmax_t) session_keyring);
fprintf(fp, "\n");
/*
* Assume the authority to instantiate the key named in argv[2].
*/
if (keyctl(KEYCTL_ASSUME_AUTHORITY, key_to_instantiate) == -1) {
fprintf(fp, "KEYCTL_ASSUME_AUTHORITY failed: %s\n",
strerror(errno));
exit(EXIT_FAILURE);
}
/*
* Fetch the description of the key that is to be instantiated.
*/
if (keyctl(KEYCTL_DESCRIBE, key_to_instantiate,
dbuf, sizeof(dbuf)) == -1) {
fprintf(fp, "KEYCTL_DESCRIBE failed: %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(fp, "Key description: %s\n", dbuf);
/*
* Fetch the payload of the authorization key, which is
* actually the callout data given to request_key().
*/
akp_size = keyctl(KEYCTL_READ, KEY_SPEC_REQKEY_AUTH_KEY,
auth_key_payload, sizeof(auth_key_payload));
if (akp_size == -1) {
fprintf(fp, "KEYCTL_READ failed: %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
auth_key_payload[akp_size] = '\0';
fprintf(fp, "Auth key payload: %s\n", auth_key_payload);
/*
* For interest, get the ID of the authorization key and
* display it.
*/
auth_key = keyctl(KEYCTL_GET_KEYRING_ID,
KEY_SPEC_REQKEY_AUTH_KEY);
if (auth_key == -1) {
fprintf(fp, "KEYCTL_GET_KEYRING_ID failed: %s\n",
strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(fp, "Auth key ID: %jx\n", (uintmax_t) auth_key);
/*
* Fetch key ID for the request_key(2) destination keyring.
*/
dest_keyring = keyctl(KEYCTL_GET_KEYRING_ID,
KEY_SPEC_REQUESTOR_KEYRING);
if (dest_keyring == -1) {
fprintf(fp, "KEYCTL_GET_KEYRING_ID failed: %s\n",
strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(fp, "Destination keyring: %jx\n", (uintmax_t) dest_keyring);
/*
* Fetch the description of the authorization key. This
* allows us to see the key type, UID, GID, permissions,
* and description (name) of the key. Among other things,
* we will see that the name of the key is a hexadecimal
* string representing the ID of the key to be instantiated.
*/
if (keyctl(KEYCTL_DESCRIBE, KEY_SPEC_REQKEY_AUTH_KEY,
dbuf, sizeof(dbuf)) == -1) {
fprintf(fp, "KEYCTL_DESCRIBE failed: %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
fprintf(fp, "Auth key description: %s\n", dbuf);
/*
* Instantiate the key using the callout data that was supplied
* in the payload of the authorization key.
*/
if (keyctl(KEYCTL_INSTANTIATE, key_to_instantiate,
auth_key_payload, akp_size + 1, dest_keyring) == -1) {
fprintf(fp, "KEYCTL_INSTANTIATE failed: %s\n",
strerror(errno));
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
