linux-ext4 - Re: Apparent serious progressive ext4 data corruption bug in 3.6.3 (and other stable branches?)

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Date:	Sun, 28 Oct 2012 21:00:13 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Nix <nix@...eri.org.uk>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: Re: Apparent serious progressive ext4 data corruption bug in 3.6.3
 (and other stable branches?)

On Sat, Oct 27, 2012 at 05:42:07PM -0500, Eric Sandeen wrote:
> 
> It looks like the inode_bitmap_bh is being modified outside a transaction:
> 
>                 ret2 = ext4_test_and_set_bit(ino, inode_bitmap_bh->b_data);
> 
> It needs a get_write_access / handle_dirty_metadata pair around it.

Oops.   Nice catch!!

The patch isn't quite right, though.  We only want to call
ext4_journal_get_write_access() when we know that there is an available
bit in the bitmap.  (We could still lose the race, but in that case
the winner of the race probably grabbed the bitmap block first.)

Also, we only need to call ext4_handle_dirty_metadata() if we
successfully grab the bit in the bitmap.

So I suggest this patch instead:

commit 087eda81f1ac6a6a0394f781b44f1d555d8f64c6
Author: Eric Sandeen <sandeen@...hat.com>
Date:   Sun Oct 28 20:59:57 2012 -0400

    ext4: fix unjournaled inode bitmap modification
    
    commit 119c0d4460b001e44b41dcf73dc6ee794b98bd31 modified this function
    such that the inode bitmap was being modified outside a transaction,
    which could lead to corruption, and was discovered when journal_checksum
    found a bad checksum in the journal.
    
    Reported-by: Nix <nix@...eri.org.uk>
    Signed-off-by: Eric Sandeen <sandeen@...hat.com>
    Signed-off-by: "Theodore Ts'o" <tytso@....edu>
    Cc: stable@...r.kernel.org

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 4facdd2..575afac 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -725,6 +725,10 @@ repeat_in_this_group:
 				   "inode=%lu", ino + 1);
 			continue;
 		}
+		BUFFER_TRACE(inode_bitmap_bh, "get_write_access");
+		err = ext4_journal_get_write_access(handle, inode_bitmap_bh);
+		if (err)
+			goto fail;
 		ext4_lock_group(sb, group);
 		ret2 = ext4_test_and_set_bit(ino, inode_bitmap_bh->b_data);
 		ext4_unlock_group(sb, group);
@@ -738,6 +742,11 @@ repeat_in_this_group:
 	goto out;
 
 got:
+	BUFFER_TRACE(inode_bitmap_bh, "call ext4_handle_dirty_metadata");
+	err = ext4_handle_dirty_metadata(handle, NULL, inode_bitmap_bh);
+	if (err)
+		goto fail;
+
 	/* We may have to initialize the block bitmap if it isn't already */
 	if (ext4_has_group_desc_csum(sb) &&
 	    gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
--
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