linux-kernel - [PATCH 3.12 63/72] KEYS: Fix race between key destruction and finding a keyring by name

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Message-Id: <f4562591c143cc272eab0d95be01dcca528627b9.1448283890.git.jslaby@suse.cz>
Date:	Mon, 23 Nov 2015 14:12:24 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 63/72] KEYS: Fix race between key destruction and finding a keyring by name

From: David Howells <dhowells@...hat.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...hat.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 797818695c87..483ebdf9c383 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -187,6 +187,10 @@ 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 */
@@ -201,10 +205,6 @@ 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);
-- 
2.6.3

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