[PATCH] Error during attempt to join key management session can leave semaphore pinned

The attached patch prevents an error during the key session joining operation
from hanging future joins in the D state [CAN-2005-2098].

The problem is that the error handling path for the KEYCTL_JOIN_SESSION_KEYRING
operation has one error path that doesn't release the session management
semaphore. Further attempts to get the semaphore will then sleep for ever in
the D state.

This can happen in four situations, all involving an attempt to allocate a new
session keyring:

(1) ENOMEM.

(2) The users key quota being reached.

(3) A keyring name that is an empty string.

(4) A keyring name that is too long.

Any user may attempt this operation, and so any user can cause the problem to
occur.

Signed-Off-By: David Howells <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

security/keys/process_keys.c

···
 		keyring = keyring_alloc(name, tsk->uid, tsk->gid, 0, NULL);
 		if (IS_ERR(keyring)) {
 			ret = PTR_ERR(keyring);
-			goto error;
+			goto error2;
 		}
 	}
 	else if (IS_ERR(keyring)) {