linux-kernel - [163/165] ext4: fix possible use-after-free in

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Date:	Wed, 01 Jun 2011 17:12:13 +0900
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Lukas Czerner <lczerner@...hat.com>,
	"Theodore Tso" <tytso@....edu>, Greg Kroah-Hartman <gregkh@...e.de>
Subject: [163/165] ext4: fix possible use-after-free in

2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------
 ext4_remove_li_request()
Content-Length: 1306
Lines: 43

From: Lukas Czerner <lczerner@...hat.com>

commit 1bb933fb1fa8e4cb337a0d5dfd2ff4c0dc2073e8 upstream.

We need to take reference to the s_li_request after we take a mutex,
because it might be freed since then, hence result in accessing old
already freed memory. Also we should protect the whole
ext4_remove_li_request() because ext4_li_info might be in the process of
being freed in ext4_lazyinit_thread().

Signed-off-by: Lukas Czerner <lczerner@...hat.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Reviewed-by: Eric Sandeen <sandeen@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/ext4/super.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2730,14 +2730,16 @@ static void ext4_remove_li_request(struc
 
 static void ext4_unregister_li_request(struct super_block *sb)
 {
-	struct ext4_li_request *elr = EXT4_SB(sb)->s_li_request;
-
-	if (!ext4_li_info)
+	mutex_lock(&ext4_li_mtx);
+	if (!ext4_li_info) {
+		mutex_unlock(&ext4_li_mtx);
 		return;
+	}
 
 	mutex_lock(&ext4_li_info->li_list_mtx);
-	ext4_remove_li_request(elr);
+	ext4_remove_li_request(EXT4_SB(sb)->s_li_request);
 	mutex_unlock(&ext4_li_info->li_list_mtx);
+	mutex_unlock(&ext4_li_mtx);
 }
 
 static struct task_struct *ext4_lazyinit_task;


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