[4.2.y-ckt stable] Patch "KEYS: Fix race between key destruction and finding a keyring by name" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 6d065dca92a84e544ea0913cb10991a4f1f86afd Mon Sep 17 00:00:00 2001
From: David Howells <dhowells at redhat.com>
Date: Fri, 25 Sep 2015 16:30:08 +0100
Subject: KEYS: Fix race between key destruction and finding a keyring by name

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 at redhat.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 security/keys/gc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index c795237..39eac1f 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -134,6 +134,10 @@ static noinline void key_gc_unused_keys(struct list_head *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(struct list_head *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);
--
1.9.1