From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0611DC38142 for ; Fri, 20 Jan 2023 02:53:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229646AbjATCxL (ORCPT ); Thu, 19 Jan 2023 21:53:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229453AbjATCxI (ORCPT ); Thu, 19 Jan 2023 21:53:08 -0500 Received: from smtp-fw-80006.amazon.com (smtp-fw-80006.amazon.com [99.78.197.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B17D29B132 for ; Thu, 19 Jan 2023 18:53:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1674183188; x=1705719188; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=UmpmDQi7bJR8lLmmf/naNO35e+8Lm9tQqbSe2Rv16PQ=; b=RDVj8rITLGmUIM2uu63zJEFzJ2vqt659ENiyy4mzx5AiWWe5gYI+RpjJ 5X52iKdIDPWtJ6niTm5M5Aa+ElFtWgy4xPEySGVAvXEpPllq1eZzWbkXJ hH2F8vcOOS/cKPN7kCdkVt1BrQlcAMD9rX8eKNVOMGDB4gYpdL0Ik20zl k=; X-IronPort-AV: E=Sophos;i="5.97,230,1669075200"; d="scan'208";a="173026157" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO email-inbound-relay-iad-1d-m6i4x-f05d30a1.us-east-1.amazon.com) ([10.25.36.210]) by smtp-border-fw-80006.pdx80.corp.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jan 2023 02:53:07 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1d-m6i4x-f05d30a1.us-east-1.amazon.com (Postfix) with ESMTPS id 53DE281DF1; Fri, 20 Jan 2023 02:53:04 +0000 (UTC) Received: from EX19D010UWA004.ant.amazon.com (10.13.138.204) by EX13MTAUWB001.ant.amazon.com (10.43.161.249) with Microsoft SMTP Server (TLS) id 15.0.1497.45; Fri, 20 Jan 2023 02:53:03 +0000 Received: from u9aa42af9e4c55a.ant.amazon.com (10.43.162.56) by EX19D010UWA004.ant.amazon.com (10.13.138.204) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.2.1118.7; Fri, 20 Jan 2023 02:53:03 +0000 From: Munehisa Kamata To: CC: , , , , , , , Subject: Re: another use-after-free in ep_remove_wait_queue() Date: Thu, 19 Jan 2023 18:52:53 -0800 Message-ID: <20230120025253.843079-1-kamatam@amazon.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230120024613.840905-1-kamatam@amazon.com> References: <20230120024613.840905-1-kamatam@amazon.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.43.162.56] X-ClientProxiedBy: EX13D38UWB001.ant.amazon.com (10.43.161.10) To EX19D010UWA004.ant.amazon.com (10.13.138.204) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2023-01-20 02:46:13 +0000, Munehisa Kamata wrote: > > On Fri, 2023-01-20 01:37:11 +0000, Suren Baghdasaryan wrote: > > > > On Thu, Jan 19, 2023 at 5:31 PM Hillf Danton wrote: > > > > > > On Thu, 19 Jan 2023 13:01:42 -0800 Suren Baghdasaryan wrote: > > > > > > > > Hi Folks, > > > > I spent some more time digging into the details and this is what's > > > > happening. When we call rmdir to delete the cgroup with the pressure > > > > file being epoll'ed, roughly the following call chain happens in the > > > > context of the shell process: > > > > > > > > do_rmdir > > > > cgroup_rmdir > > > > kernfs_drain_open_files > > > > cgroup_file_release > > > > cgroup_pressure_release > > > > psi_trigger_destroy > > > > > > > > Later on in the context of our reproducer, the last fput() is called > > > > causing wait queue removal: > > > > > > > > fput > > > > ep_eventpoll_release > > > > ep_free > > > > ep_remove_wait_queue > > > > remove_wait_queue > > > > > > > > By this time psi_trigger_destroy() already destroyed the trigger's > > > > waitqueue head and we hit UAF. > > > > I think the conceptual problem here (or maybe that's by design?) is > > > > that cgroup_file_release() is not really tied to the file's real > > > > lifetime (when the last fput() is issued). Otherwise fput() would call > > > > eventpoll_release() before f_op->release() and the order would be fine > > > > (we would remove the wait queue first in eventpoll_release() and then > > > > f_op->release() would cause trigger's destruction). > > > > > > eventpoll_release > > > eventpoll_release_file > > > ep_remove > > > ep_unregister_pollwait > > > ep_remove_wait_queue > > > > > > > Yes but fput() calls eventpoll_release() *before* f_op->release(), so > > waitqueue_head would be removed before trigger destruction. > > But pwq->whead is still pointing the freed head, then we just hit the same > issue earlier? Ah nevermind, that was just a hypothetical case if cgroup_file_release() was tied to file's lifetime and assuming trigger destruction that frees the queue and clears pwq->whead would happen later in f_op->release(); there is no such an implementation today. Sorry for noise. > > > Different roads run into the same Roma city. > > > > You butchered the phrase :) > > > > > > > > > Considering these findings, I think we can use the wake_up_pollfree() > > > > without contradicting the comment at > > > > https://elixir.bootlin.com/linux/latest/source/include/linux/wait.h#L253 > > > > because indeed, cgroup_file_release() and therefore > > > > psi_trigger_destroy() are not tied to the file's lifetime. > > > > > > > > I'm CC'ing Tejun to check if this makes sense to him and > > > > cgroup_file_release() is working as expected in this case. > > > > > > > > Munehisha, if Tejun confirms this is all valid, could you please post > > > > a patch replacing wake_up_interruptible() with wake_up_pollfree()? We > > > > don't need to worry about wake_up_all() because we have a limitation > > > > of one trigger per file descriptor: > > > > https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L1419, > > > > so there can be only one waiter. > > > > Thanks, > > > > Suren. > > > > > > > > >