linux-kernel - [PATCH 3.4 134/176] KEYS: close race between key lookup and freeing

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Message-Id: <1428569224-23820-134-git-send-email-lizf@kernel.org>
Date:	Thu,  9 Apr 2015 16:46:22 +0800
From:	lizf@...nel.org
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Sasha Levin <sasha.levin@...cle.com>,
	David Howells <dhowells@...hat.com>,
	Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 134/176] KEYS: close race between key lookup and freeing

From: Sasha Levin <sasha.levin@...cle.com>

3.4.107-rc1 review patch.  If anyone has any objections, please let me know.

------------------


commit a3a8784454692dd72e5d5d34dcdab17b4420e74c upstream.

When a key is being garbage collected, it's key->user would get put before
the ->destroy() callback is called, where the key is removed from it's
respective tracking structures.

This leaves a key hanging in a semi-invalid state which leaves a window open
for a different task to try an access key->user. An example is
find_keyring_by_name() which would dereference key->user for a key that is
in the process of being garbage collected (where key->user was freed but
->destroy() wasn't called yet - so it's still present in the linked list).

This would cause either a panic, or corrupt memory.

Fixes CVE-2014-9529.

Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
Signed-off-by: David Howells <dhowells@...hat.com>
[lizf: Backported to 3.4: adjust indentation]
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 security/keys/gc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index a42b455..87632bd 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -188,12 +188,12 @@ static noinline void key_gc_unused_key(struct key *key)
 	if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 		atomic_dec(&key->user->nikeys);
 
-	key_user_put(key->user);
-
 	/* now throw away the key memory */
 	if (key->type->destroy)
 		key->type->destroy(key);
 
+	key_user_put(key->user);
+
 	kfree(key->description);
 
 #ifdef KEY_DEBUGGING
-- 
1.9.1

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