9p: Skip check for mandatory locks when unlocking

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@redhat.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Cc: maximilian attems <max@stro.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 3902bf43a0883bfe4b92d384170362e53c910e0d..5fb43bd19688a11e5c55a6ca1b00713344a93daa 100644 (file)
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -114,7 +114,7 @@ static int v9fs_file_lock(struct file *filp, int cmd, struct file_lock *fl)
        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) {