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

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

From: Arthur Jones

commit c87591b719737b4e91eb1a9fa8fd55a4ff1886d6 upstream

In ext3_sync_fs, we only wait for a commit to finish if we started it, but
there may be one already in progress which will not be synced.

In the case of a data=ordered umount with pending long symlinks which are
delayed due to a long list of other I/O on the backing block device, this
causes the buffer associated with the long symlinks to not be moved to the
inode dirty list in the second phase of fsync_super. Then, before they
can be dirtied again, kjournald exits, seeing the UMOUNT flag and the
dirty pages are never written to the backing block device, causing long
symlink corruption and exposing new or previously freed block data to
userspace.

This can be reproduced with a script created
by Eric Sandeen :

#!/bin/bash

umount /mnt/test2
mount /dev/sdb4 /mnt/test2
rm -f /mnt/test2/*
dd if=/dev/zero of=/mnt/test2/bigfile bs=1M count=512
touch
/mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryvery veryveryveryveryverylongfilename
ln -s
/mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryvery veryveryveryveryverylongfilename
/mnt/test2/link
umount /mnt/test2
mount /dev/sdb4 /mnt/test2
ls /mnt/test2/
umount /mnt/test2

To ensure all commits are synced, we flush all journal commits now when
sync_fs'ing ext3.

Signed-off-by: Arthur Jones
Cc: Eric Sandeen
Cc: Theodore Ts'o
Cc:
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
Signed-off-by: Greg Kroah-Hartman

---
fs/ext3/super.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -2365,13 +2365,12 @@ static void ext3_write_super (struct sup

static int ext3_sync_fs(struct super_block *sb, int wait)
{
- tid_t target;
-
sb->s_dirt = 0;
- if (journal_start_commit(EXT3_SB(sb)->s_journal, &target)) {
- if (wait)
- log_wait_commit(EXT3_SB(sb)->s_journal, target);
- }
+ if (wait)
+ ext3_force_commit(sb);
+ else
+ journal_start_commit(EXT3_SB(sb)->s_journal, NULL);
+
return 0;
}


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