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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 541AFCA9EA0 for ; Mon, 28 Oct 2019 09:18:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C0F521783 for ; Mon, 28 Oct 2019 09:18:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387894AbfJ1JSk (ORCPT ); Mon, 28 Oct 2019 05:18:40 -0400 Received: from mx2.suse.de ([195.135.220.15]:57538 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727664AbfJ1JSj (ORCPT ); Mon, 28 Oct 2019 05:18:39 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 5496BB009; Mon, 28 Oct 2019 09:18:37 +0000 (UTC) Date: Mon, 28 Oct 2019 09:18:36 +0000 From: Luis Henriques To: Jeff Layton Cc: Sage Weil , Ilya Dryomov , "Yan, Zheng" , ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] ceph: Fix use-after-free in __ceph_remove_cap Message-ID: <20191028091836.GA8558@hermes.olymp> References: <9c1fe73500ca7dece15c73d7534b9e0ec417c83a.camel@kernel.org> <20191025130524.31755-1-lhenriques@suse.com> <1a9ac7d3097efe53ad6f2fda4dd584204dd7eba2.camel@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1a9ac7d3097efe53ad6f2fda4dd584204dd7eba2.camel@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 27, 2019 at 08:31:49AM -0400, Jeff Layton wrote: > On Fri, 2019-10-25 at 14:05 +0100, Luis Henriques wrote: > > KASAN reports a use-after-free when running xfstest generic/531, with the > > following trace: > > > > [ 293.903362] kasan_report+0xe/0x20 > > [ 293.903365] rb_erase+0x1f/0x790 > > [ 293.903370] __ceph_remove_cap+0x201/0x370 > > [ 293.903375] __ceph_remove_caps+0x4b/0x70 > > [ 293.903380] ceph_evict_inode+0x4e/0x360 > > [ 293.903386] evict+0x169/0x290 > > [ 293.903390] __dentry_kill+0x16f/0x250 > > [ 293.903394] dput+0x1c6/0x440 > > [ 293.903398] __fput+0x184/0x330 > > [ 293.903404] task_work_run+0xb9/0xe0 > > [ 293.903410] exit_to_usermode_loop+0xd3/0xe0 > > [ 293.903413] do_syscall_64+0x1a0/0x1c0 > > [ 293.903417] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > This happens because __ceph_remove_cap() may queue a cap release > > (__ceph_queue_cap_release) which can be scheduled before that cap is > > removed from the inode list with > > > > rb_erase(&cap->ci_node, &ci->i_caps); > > > > And, when this finally happens, the use-after-free will occur. > > > > This can be fixed by removing the cap from the inode list before being > > removed from the session list, and thus eliminating the risk of an UAF. > > > > Signed-off-by: Luis Henriques > > --- > > Hi! > > > > So, after spending some time trying to find possible races throught code > > review and testing, I modified the fix according to Jeff's suggestion. > > > > Cheers, > > Luis > > > > fs/ceph/caps.c | 10 +++++----- > > 1 file changed, 5 insertions(+), 5 deletions(-) > > > > diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c > > index d3b9c9d5c1bd..a9ce858c37d0 100644 > > --- a/fs/ceph/caps.c > > +++ b/fs/ceph/caps.c > > @@ -1058,6 +1058,11 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release) > > > > dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode); > > > > + /* remove from inode list */ > > + rb_erase(&cap->ci_node, &ci->i_caps); > > + if (ci->i_auth_cap == cap) > > + ci->i_auth_cap = NULL; > > + > > /* remove from session list */ > > spin_lock(&session->s_cap_lock); > > if (session->s_cap_iterator == cap) { > > @@ -1091,11 +1096,6 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release) > > > > spin_unlock(&session->s_cap_lock); > > > > - /* remove from inode list */ > > - rb_erase(&cap->ci_node, &ci->i_caps); > > - if (ci->i_auth_cap == cap) > > - ci->i_auth_cap = NULL; > > - > > if (removed) > > ceph_put_cap(mdsc, cap); > > > > Looks good. Merged with a slight modification to the comment: > > + /* remove from inode's cap rbtree, and clear auth cap */ > Awesome, thanks. Regarding CC: stable@, feel free to add that too. I guess it makes sense, even if this issue has been there for a while apparently without any reports. (Although UAFs may have non-obvious side effects, I guess...) Cheers, -- Luís > Thanks! > -- > Jeff Layton >