Patch "KEYS: Fix race between key destruction and finding a keyring by name" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KEYS: Fix race between key destruction and finding a keyring by name

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     keys-fix-race-between-key-destruction-and-finding-a-keyring-by-name.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 94c4554ba07adbdde396748ee7ae01e86cf2d8d7 Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@redhat.com>
Date: Fri, 25 Sep 2015 16:30:08 +0100
Subject: KEYS: Fix race between key destruction and finding a keyring by name

From: David Howells <dhowells@redhat.com>

commit 94c4554ba07adbdde396748ee7ae01e86cf2d8d7 upstream.

There appears to be a race between:

 (1) key_gc_unused_keys() which frees key->security and then calls
     keyring_destroy() to unlink the name from the name list

 (2) find_keyring_by_name() which calls key_permission(), thus accessing
     key->security, on a key before checking to see whether the key usage is 0
     (ie. the key is dead and might be cleaned up).

Fix this by calling ->destroy() before cleaning up the core key data -
including key->security.

Reported-by: Petr Matousek <pmatouse@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 security/keys/gc.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -134,6 +134,10 @@ static noinline void key_gc_unused_keys(
 		kdebug("- %u", key->serial);
 		key_check(key);
 
+		/* Throw away the key data */
+		if (key->type->destroy)
+			key->type->destroy(key);
+
 		security_key_free(key);
 
 		/* deal with the user's key tracking and quota */
@@ -148,10 +152,6 @@ static noinline void key_gc_unused_keys(
 		if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 			atomic_dec(&key->user->nikeys);
 
-		/* now throw away the key memory */
-		if (key->type->destroy)
-			key->type->destroy(key);
-
 		key_user_put(key->user);
 
 		kfree(key->description);


Patches currently in stable-queue which might be from dhowells@redhat.com are

queue-4.1/keys-fix-keyring-ref-leak-in-join_session_keyring.patch
queue-4.1/keys-fix-crash-when-attempt-to-garbage-collect-an-uninstantiated-keyring.patch
queue-4.1/keys-fix-race-between-read-and-revoke.patch
queue-4.1/keys-fix-race-between-key-destruction-and-finding-a-keyring-by-name.patch
queue-4.1/keys-refcount-bug-fix.patch
queue-4.1/keys-prevent-keys-from-being-removed-from-specified-keyrings.patch