[ 3.5.y.z extended stable ] Patch "ext4: fix possible use after free with metadata csum" has been added to staging queue

[Herton Ronaldo Krzesinski]

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

    ext4: fix possible use after free with metadata csum

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

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

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From 16ccd8707d47c4c168e3d625891e7f41bacba2bc Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso at mit.edu>
Date: Thu, 29 Nov 2012 21:21:22 -0500
Subject: [PATCH] ext4: fix possible use after free with metadata csum

commit aeb1e5d69a5be592e86a926be73efb38c55af404 upstream.

Commit fa77dcfafeaa introduces block bitmap checksum calculation into
ext4_new_inode() in the case that block group was uninitialized.
However we brelse() the bitmap buffer before we attempt to checksum it
so we have no guarantee that the buffer is still there.

Fix this by releasing the buffer after the possible checksum
computation.

Signed-off-by: Lukas Czerner <lczerner at redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Acked-by: Darrick J. Wong <darrick.wong at oracle.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 fs/ext4/ialloc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 4418852..536ac65 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -754,7 +754,6 @@ got:

 		BUFFER_TRACE(block_bitmap_bh, "dirty block bitmap");
 		err = ext4_handle_dirty_metadata(handle, NULL, block_bitmap_bh);
-		brelse(block_bitmap_bh);

 		/* recheck and clear flag under lock if we still need to */
 		ext4_lock_group(sb, group);
@@ -767,6 +766,7 @@ got:
 			ext4_group_desc_csum_set(sb, group, gdp);
 		}
 		ext4_unlock_group(sb, group);
+		brelse(block_bitmap_bh);

 		if (err)
 			goto fail;
--
1.7.9.5