[3.5.y.z extended stable] Patch "hpfs: deadlock and race in directory lseek()" has been added to staging queue

[Luis Henriques]

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

    hpfs: deadlock and race in directory lseek()

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.
-Luis

------

>From 2b2b9717c556dad74035c9edb35e66b2c8eeaa52 Mon Sep 17 00:00:00 2001
From: Al Viro <viro at zeniv.linux.org.uk>
Date: Sat, 18 May 2013 02:38:52 -0400
Subject: hpfs: deadlock and race in directory lseek()

commit 31abdab9c11bb1694ecd1476a7edbe8e964d94ac upstream.

For one thing, there's an ABBA deadlock on hpfs fs-wide lock and i_mutex
in hpfs_dir_lseek() - there's a lot of methods that grab the former with
the caller already holding the latter, so it must take i_mutex first.

For another, locking the damn thing, carefully validating the offset,
then dropping locks and assigning the offset is obviously racy.

Moreover, we _must_ do hpfs_add_pos(), or the machinery in dnode.c
won't modify the sucker on B-tree surgeries.

Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Cc: Mikulas Patocka <mikulas at artax.karlin.mff.cuni.cz>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/hpfs/dir.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/hpfs/dir.c b/fs/hpfs/dir.c
index b8472f8..ea2b23c5 100644
--- a/fs/hpfs/dir.c
+++ b/fs/hpfs/dir.c
@@ -33,25 +33,27 @@ static loff_t hpfs_dir_lseek(struct file *filp, loff_t off, int whence)
 	if (whence == SEEK_DATA || whence == SEEK_HOLE)
 		return -EINVAL;

+	mutex_lock(&i->i_mutex);
 	hpfs_lock(s);

 	/*printk("dir lseek\n");*/
 	if (new_off == 0 || new_off == 1 || new_off == 11 || new_off == 12 || new_off == 13) goto ok;
-	mutex_lock(&i->i_mutex);
 	pos = ((loff_t) hpfs_de_as_down_as_possible(s, hpfs_inode->i_dno) << 4) + 1;
 	while (pos != new_off) {
 		if (map_pos_dirent(i, &pos, &qbh)) hpfs_brelse4(&qbh);
 		else goto fail;
 		if (pos == 12) goto fail;
 	}
-	mutex_unlock(&i->i_mutex);
+	hpfs_add_pos(i, &filp->f_pos);
 ok:
+	filp->f_pos = new_off;
 	hpfs_unlock(s);
-	return filp->f_pos = new_off;
-fail:
 	mutex_unlock(&i->i_mutex);
+	return new_off;
+fail:
 	/*printk("illegal lseek: %016llx\n", new_off);*/
 	hpfs_unlock(s);
+	mutex_unlock(&i->i_mutex);
 	return -ESPIPE;
 }

--
1.9.1