linux-kernel - [130/197] 9p: Skip check for mandatory locks when unlocking

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Date:	Thu, 22 Apr 2010 12:09:41 -0700
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,
	Sachin Prabhu <sprabhu@...hat.com>,
	Eric Van Hensbergen <ericvh@...il.com>,
	maximilian attems <max@...o.at>
Subject: [130/197] 9p: Skip check for mandatory locks when unlocking

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

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

From: Sachin Prabhu <sprabhu@...hat.com>

commit f78233dd44a110c574fe760ad6f9c1e8741a0d00 upstream.

While investigating a bug, I came across a possible bug in v9fs. The
problem is similar to the one reported for NFS by ASANO Masahiro in
http://lkml.org/lkml/2005/12/21/334.

v9fs_file_lock() will skip locks on file which has mode set to 02666.
This is a problem in cases where the mode of the file is changed after
a process has obtained a lock on the file. Such a lock will be skipped
during unlock and the machine will end up with a BUG in
locks_remove_flock().

v9fs_file_lock() should skip the check for mandatory locks when
unlocking a file.

Signed-off-by: Sachin Prabhu <sprabhu@...hat.com>
Signed-off-by: Eric Van Hensbergen <ericvh@...il.com>
Cc: maximilian attems <max@...o.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/9p/vfs_file.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -114,7 +114,7 @@ static int v9fs_file_lock(struct file *f
 	P9_DPRINTK(P9_DEBUG_VFS, "filp: %p lock: %p\n", filp, fl);

 	/* No mandatory locks */
-	if (__mandatory_lock(inode))
+	if (__mandatory_lock(inode) && fl->fl_type != F_UNLCK)
 		return -ENOLCK;

 	if ((IS_SETLK(cmd) || IS_SETLKW(cmd)) && fl->fl_type != F_UNLCK) {

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