[PATCH] KEYS: Fix keyring ref leak in join_session_keyring()

[PATCH] KEYS: Fix keyring ref leak in join_session_keyring()

[David Howells]

From: Yevgeny Pats <yevgeny@perception-point.io>

This fixes CVE-2016-0728.

If a thread is asked to join as a session keyring the keyring that's already
set as its session, we leak a keyring reference.

This can be tested with the following program:

	#include <stddef.h>
	#include <stdio.h>
	#include <sys/types.h>
	#include <keyutils.h>

	int main(int argc, const char *argv[])
	{
		int i = 0;
		key_serial_t serial;

		serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING,
				"leaked-keyring");
		if (serial < 0) {
			perror("keyctl");
			return -1;
		}

		if (keyctl(KEYCTL_SETPERM, serial,
			   KEY_POS_ALL | KEY_USR_ALL) < 0) {
			perror("keyctl");
			return -1;
		}

		for (i = 0; i < 100; i++) {
			serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING,
					"leaked-keyring");
			if (serial < 0) {
				perror("keyctl");
				return -1;
			}
		}

		return 0;
	}

If, after the program has run, there something like the following line in
/proc/keys:

3f3d898f I--Q---   100 perm 3f3f0000     0     0 keyring   leaked-keyring: empty

with a usage count of 100 * the number of times the program has been run,
then the kernel is malfunctioning.  If leaked-keyring has zero usages or
has been garbage collected, then the problem is fixed.

Reported-by: Yevgeny Pats <yevgeny@perception-point.io>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
---

 security/keys/process_keys.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index a3f85d2a00bb..e6d50172872f 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -794,6 +794,7 @@ long join_session_keyring(const char *name)
 		ret = PTR_ERR(keyring);
 		goto error2;
 	} else if (keyring == new->session_keyring) {
+		key_put(keyring);
 		ret = 0;
 		goto error2;
 	}

Re: [PATCH] KEYS: Fix keyring ref leak in join_session_keyring()

[Greg KH]

On Tue, Jan 19, 2016 at 10:09:04PM +0000, David Howells wrote:
> From: Yevgeny Pats <yevgeny@perception-point.io>
> 
> This fixes CVE-2016-0728.
> 
> If a thread is asked to join as a session keyring the keyring that's already
> set as its session, we leak a keyring reference.
> 
> This can be tested with the following program:
> 
> 	#include <stddef.h>
> 	#include <stdio.h>
> 	#include <sys/types.h>
> 	#include <keyutils.h>
> 
> 	int main(int argc, const char *argv[])
> 	{
> 		int i = 0;
> 		key_serial_t serial;
> 
> 		serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING,
> 				"leaked-keyring");
> 		if (serial < 0) {
> 			perror("keyctl");
> 			return -1;
> 		}
> 
> 		if (keyctl(KEYCTL_SETPERM, serial,
> 			   KEY_POS_ALL | KEY_USR_ALL) < 0) {
> 			perror("keyctl");
> 			return -1;
> 		}
> 
> 		for (i = 0; i < 100; i++) {
> 			serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING,
> 					"leaked-keyring");
> 			if (serial < 0) {
> 				perror("keyctl");
> 				return -1;
> 			}
> 		}
> 
> 		return 0;
> 	}
> 
> If, after the program has run, there something like the following line in
> /proc/keys:
> 
> 3f3d898f I--Q---   100 perm 3f3f0000     0     0 keyring   leaked-keyring: empty
> 
> with a usage count of 100 * the number of times the program has been run,
> then the kernel is malfunctioning.  If leaked-keyring has zero usages or
> has been garbage collected, then the problem is fixed.
> 
> Reported-by: Yevgeny Pats <yevgeny@perception-point.io>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Acked-by: Don Zickus <dzickus@redhat.com>
> Acked-by: Prarit Bhargava <prarit@redhat.com>
> Acked-by: Jarod Wilson <jarod@redhat.com>

Any reason you didn't tag this for stable kernels?

thanks,

greg k-h

Re: [PATCH] KEYS: Fix keyring ref leak in join_session_keyring()

[David Howells]

Greg KH <gregkh@linuxfoundation.org> wrote:

> Any reason you didn't tag this for stable kernels?

Sorry, I forgot.

David