From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932935Ab3GZV2N (ORCPT ); Fri, 26 Jul 2013 17:28:13 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:50831 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760005Ab3GZUs5 (ORCPT ); Fri, 26 Jul 2013 16:48:57 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, David Jeffery , Bryan Schumaker , "J. Bruce Fields" Subject: [ 75/79] lockd: protect nlm_blocked access in nlmsvc_retry_blocked Date: Fri, 26 Jul 2013 13:48:05 -0700 Message-Id: <20130726204730.689103566@linuxfoundation.org> X-Mailer: git-send-email 1.8.3.rc0.20.gb99dd2e In-Reply-To: <20130726204721.849052763@linuxfoundation.org> References: <20130726204721.849052763@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Jeffery commit 1c327d962fc420aea046c16215a552710bde8231 upstream. In nlmsvc_retry_blocked, the check that the list is non-empty and acquiring the pointer of the first entry is unprotected by any lock. This allows a rare race condition when there is only one entry on the list. A function such as nlmsvc_grant_callback() can be called, which will temporarily remove the entry from the list. Between the list_empty() and list_entry(),the list may become empty, causing an invalid pointer to be used as an nlm_block, leading to a possible crash. This patch adds the nlm_block_lock around these calls to prevent concurrent use of the nlm_blocked list. This was a regression introduced by f904be9cc77f361d37d71468b13ff3d1a1823dea "lockd: Mostly remove BKL from the server". Signed-off-by: David Jeffery Cc: Bryan Schumaker Signed-off-by: J. Bruce Fields Signed-off-by: Greg Kroah-Hartman --- fs/lockd/svclock.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/fs/lockd/svclock.c +++ b/fs/lockd/svclock.c @@ -939,6 +939,7 @@ nlmsvc_retry_blocked(void) unsigned long timeout = MAX_SCHEDULE_TIMEOUT; struct nlm_block *block; + spin_lock(&nlm_blocked_lock); while (!list_empty(&nlm_blocked) && !kthread_should_stop()) { block = list_entry(nlm_blocked.next, struct nlm_block, b_list); @@ -948,6 +949,7 @@ nlmsvc_retry_blocked(void) timeout = block->b_when - jiffies; break; } + spin_unlock(&nlm_blocked_lock); dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n", block, block->b_when); @@ -957,7 +959,9 @@ nlmsvc_retry_blocked(void) retry_deferred_block(block); } else nlmsvc_grant_blocked(block); + spin_lock(&nlm_blocked_lock); } + spin_unlock(&nlm_blocked_lock); return timeout; }