From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763496AbXIKMl1 (ORCPT ); Tue, 11 Sep 2007 08:41:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762460AbXIKMlU (ORCPT ); Tue, 11 Sep 2007 08:41:20 -0400 Received: from sacred.ru ([62.205.161.221]:59173 "EHLO sacred.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762602AbXIKMlT (ORCPT ); Tue, 11 Sep 2007 08:41:19 -0400 Message-ID: <46E68C35.7040001@openvz.org> Date: Tue, 11 Sep 2007 16:38:13 +0400 From: Pavel Emelyanov User-Agent: Thunderbird 2.0.0.6 (X11/20070728) MIME-Version: 1.0 To: Trond Myklebust , "J. Bruce Fields" , Andrew Morton CC: Linux Kernel Mailing List , devel@openvz.org Subject: [PATCH] Memory shortage can result in inconsistent flocks state Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-3.0 (sacred.ru [62.205.161.221]); Tue, 11 Sep 2007 16:40:35 +0400 (MSD) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org When the flock_lock_file() is called to change the flock from F_RDLCK to F_WRLCK or vice versa the existing flock can be removed without appropriate warning. Look: for_each_lock(inode, before) { struct file_lock *fl = *before; if (IS_POSIX(fl)) break; if (IS_LEASE(fl)) continue; if (filp != fl->fl_file) continue; if (request->fl_type == fl->fl_type) goto out; found = 1; locks_delete_lock(before); <<<<<< ! break; } if after this point the subsequent locks_alloc_lock() will fail the return code will be -ENOMEM, but the existing lock is already removed. This is a known feature that such "re-locking" is not atomic, but in the racy case the file should stay locked (although by some other process), but in this case the file will be unlocked. The proposal is to prepare the lock in advance keeping no chance to fail in the future code. Found during making the flocks pid-namespaces aware. Signed-off-by: Pavel Emelyanov --- diff --git a/fs/locks.c b/fs/locks.c index 0db1a14..f59d066 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -732,6 +732,14 @@ static int flock_lock_file(struct file * lock_kernel(); if (request->fl_flags & FL_ACCESS) goto find_conflict; + + if (request->fl_type != F_UNLCK) { + error = -ENOMEM; + new_fl = locks_alloc_lock(); + if (new_fl == NULL) + goto out; + } + for_each_lock(inode, before) { struct file_lock *fl = *before; if (IS_POSIX(fl)) @@ -753,10 +761,6 @@ static int flock_lock_file(struct file * goto out; } - error = -ENOMEM; - new_fl = locks_alloc_lock(); - if (new_fl == NULL) - goto out; /* * If a higher-priority process was blocked on the old file lock, * give it the opportunity to lock the file.