Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754716AbaA1LH4 (ORCPT ); Tue, 28 Jan 2014 06:07:56 -0500 Received: from cantor2.suse.de ([195.135.220.15]:55802 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750816AbaA1LHz (ORCPT ); Tue, 28 Jan 2014 06:07:55 -0500 Date: Tue, 28 Jan 2014 12:07:51 +0100 (CET) From: Jiri Kosina To: Jan Kara cc: Dave Jones , Linus Torvalds , Linux Kernel Subject: Re: fanotify use after free. In-Reply-To: <20140128080201.GA13676@quack.suse.cz> Message-ID: References: <20140122233622.GB27916@quack.suse.cz> <20140123150540.GD28796@quack.suse.cz> <20140123235549.GA7363@quack.suse.cz> <20140127234017.GA7868@quack.suse.cz> <20140128061037.GA27636@redhat.com> <20140128080201.GA13676@quack.suse.cz> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 28 Jan 2014, Jan Kara wrote: > > 2b:* 4d 8b 64 c6 08 mov 0x8(%r14,%rax,8),%r12 <-- trapping instruction > > > > R14 is 0x6b6b6b6b6b6b6c03, which looks like a use-after-free. > Yup. But I'm somewhat puzzled by the trace. We crash when calling > fsnotify_destroy_event() from fanotify_handle_event(). The fsnotify code > has been called from do_sys_open() so the event was a 'FS_OPEN' which fails > the fsn_event->mask & FAN_ALL_PERM_EVENTS test. > > Slapping my forehead, that's a really stupid bug. The event > fsnotify_add_notify_event() returns may be freed by the time we return > because we already dropped the notification mutex. And then fsn_event->mask > & FAN_ALL_PERM_EVENTS test will pass because FAN_ALL_PERM_EVENTS matches > with the poison pattern 0x6b6b6b6b. So yet another hacked up version of > fanotify fix is attached. And I have to seriously think about use counts > for fanotify version of that struct. With the fixed version of the patch, all the fanotify-related oopses are gone on my system. -- Jiri Kosina SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/