Commit bfe86024 authored Aug 22, 2014 by Jeff Layton

locks: close potential race in lease_get_mtime



lease_get_mtime is called without the i_lock held, so there's no
guarantee about the stability of the list. Between the time when we
assign "flock" and then dereference it to check whether it's a lease
and for write, the lease could be freed.

Ensure that that doesn't occur by taking the i_lock before trying
to check the lease.

Cc: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

parent e0b93edd

fs/locks.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -1456,8 +1456,18 @@ EXPORT_SYMBOL(__break_lease);
		*/
		void lease_get_mtime(struct inode inode, struct timespec time)
		{
		struct file_lock *flock = inode->i_flock;
		bool has_lease = false;
		struct file_lock *flock;

		if (inode->i_flock) {
		spin_lock(&inode->i_lock);
		flock = inode->i_flock;
		if (flock && IS_LEASE(flock) && (flock->fl_type == F_WRLCK))
		has_lease = true;
		spin_unlock(&inode->i_lock);
		}

		if (has_lease)
		*time = current_fs_time(inode->i_sb);
		else
		*time = inode->i_mtime;