From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BEC961B21BD; Thu, 25 Sep 2025 11:44:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758800660; cv=none; b=QkbnQEAmLUnQUBuYCNje7So4M6mW5ZJtNAXvkW7Kum/ycaW0MUwAUHCRdV2wrtk2gOEeoxhbqXW6ucTex46HnCCG8Yr3Y97Icaqif2CScCl5IZWjkSAaTudTIwd/p6W5Aa3cvBt0vjBgkYGWghxUMIgrjPxr2f6cWv15UtKbI9c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758800660; c=relaxed/simple; bh=aiSmv5lJBWfdx8igifpyHlFY6FmJBKCs67+qrSa4/nE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uGveVK0kzXnK3ovCTVFRIJo/gSPuFgu7A68r6qeMkJxXUMvUm3wGT23lFoT6vJiBbOdCtMbMJ/CU2kcgleukf8Tx3i4+VqoI4YpS66b4OBUXiKvpoHcbkey6msWNSp5EoHJUfMQbM7soMLbYAyAOrKOQVkUEMIERTVyWcj/VKIk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mDS6dkOu; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mDS6dkOu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 19E1AC4CEF5; Thu, 25 Sep 2025 11:44:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758800660; bh=aiSmv5lJBWfdx8igifpyHlFY6FmJBKCs67+qrSa4/nE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mDS6dkOuYikZfn+5quIXDcfww+pT5T3dwSpNGPEy8ZViGmIZeMBDvNcoPzjlWAD90 zD+1rvXiKz1FAeykxIfPnT3lV2DLF3Vdfeu9OUnsGrC6ygvu2l3fhL+Kr168qtN76f oM5/JEvhm6AzZ7OcbweJxoS184Io2OZaraVS+BqFOIBwHmkeQ8RMN2msyViFqXvePd IM/kwapuufNCtVWEmrq0crDm+u7x0S6Wq1WnWib0mGngV3HbMRafu8VcNEWqDtCsTa XtXK/SFkUk5jv2OO5+q5+pdl0/Ykm6ZNwBdRdmEuKu/6W3oaptHxIGeBLehDbsLcqh zh1xbQ5H5XE3w== Date: Thu, 25 Sep 2025 07:44:18 -0400 From: Sasha Levin To: Lee Jones Cc: Greg Kroah-Hartman , stable@vger.kernel.org, patches@lists.linux.dev, Jann Horn , Kuniyuki Iwashima , Paolo Abeni Subject: Re: [PATCH 6.1 070/132] af_unix: Dont leave consecutive consumed OOB skbs. Message-ID: References: <20250703143939.370927276@linuxfoundation.org> <20250703143942.167088603@linuxfoundation.org> <20250925090827.GA514097@google.com> <2025092526-grandpa-rebound-6473@gregkh> <20250925104732.GB8757@google.com> <20250925104914.GC8757@google.com> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20250925104914.GC8757@google.com> On Thu, Sep 25, 2025 at 11:49:14AM +0100, Lee Jones wrote: >On Thu, 25 Sep 2025, Lee Jones wrote: > >> On Thu, 25 Sep 2025, Greg Kroah-Hartman wrote: >> >> > On Thu, Sep 25, 2025 at 10:08:27AM +0100, Lee Jones wrote: >> > > On Thu, 03 Jul 2025, Greg Kroah-Hartman wrote: >> > > >> > > > 6.1-stable review patch. If anyone has any objections, please let me know. >> > > > >> > > > ------------------ >> > > > >> > > > From: Kuniyuki Iwashima >> > > > >> > > > [ Upstream commit 32ca245464e1479bfea8592b9db227fdc1641705 ] >> > > > >> > > > Jann Horn reported a use-after-free in unix_stream_read_generic(). >> > > > >> > > > The following sequences reproduce the issue: >> > > > >> > > > $ python3 >> > > > from socket import * >> > > > s1, s2 = socketpair(AF_UNIX, SOCK_STREAM) >> > > > s1.send(b'x', MSG_OOB) >> > > > s2.recv(1, MSG_OOB) # leave a consumed OOB skb >> > > > s1.send(b'y', MSG_OOB) >> > > > s2.recv(1, MSG_OOB) # leave a consumed OOB skb >> > > > s1.send(b'z', MSG_OOB) >> > > > s2.recv(1) # recv 'z' illegally >> > > > s2.recv(1, MSG_OOB) # access 'z' skb (use-after-free) >> > > > >> > > > Even though a user reads OOB data, the skb holding the data stays on >> > > > the recv queue to mark the OOB boundary and break the next recv(). >> > > > >> > > > After the last send() in the scenario above, the sk2's recv queue has >> > > > 2 leading consumed OOB skbs and 1 real OOB skb. >> > > > >> > > > Then, the following happens during the next recv() without MSG_OOB >> > > > >> > > > 1. unix_stream_read_generic() peeks the first consumed OOB skb >> > > > 2. manage_oob() returns the next consumed OOB skb >> > > > 3. unix_stream_read_generic() fetches the next not-yet-consumed OOB skb >> > > > 4. unix_stream_read_generic() reads and frees the OOB skb >> > > > >> > > > , and the last recv(MSG_OOB) triggers KASAN splat. >> > > > >> > > > The 3. above occurs because of the SO_PEEK_OFF code, which does not >> > > > expect unix_skb_len(skb) to be 0, but this is true for such consumed >> > > > OOB skbs. >> > > > >> > > > while (skip >= unix_skb_len(skb)) { >> > > > skip -= unix_skb_len(skb); >> > > > skb = skb_peek_next(skb, &sk->sk_receive_queue); >> > > > ... >> > > > } >> > > > >> > > > In addition to this use-after-free, there is another issue that >> > > > ioctl(SIOCATMARK) does not function properly with consecutive consumed >> > > > OOB skbs. >> > > > >> > > > So, nothing good comes out of such a situation. >> > > > >> > > > Instead of complicating manage_oob(), ioctl() handling, and the next >> > > > ECONNRESET fix by introducing a loop for consecutive consumed OOB skbs, >> > > > let's not leave such consecutive OOB unnecessarily. >> > > > >> > > > Now, while receiving an OOB skb in unix_stream_recv_urg(), if its >> > > > previous skb is a consumed OOB skb, it is freed. >> > > > >> > > > [0]: >> > > > BUG: KASAN: slab-use-after-free in unix_stream_read_actor (net/unix/af_unix.c:3027) >> > > > Read of size 4 at addr ffff888106ef2904 by task python3/315 >> > > > >> > > > CPU: 2 UID: 0 PID: 315 Comm: python3 Not tainted 6.16.0-rc1-00407-gec315832f6f9 #8 PREEMPT(voluntary) >> > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-4.fc42 04/01/2014 >> > > > Call Trace: >> > > > >> > > > dump_stack_lvl (lib/dump_stack.c:122) >> > > > print_report (mm/kasan/report.c:409 mm/kasan/report.c:521) >> > > > kasan_report (mm/kasan/report.c:636) >> > > > unix_stream_read_actor (net/unix/af_unix.c:3027) >> > > > unix_stream_read_generic (net/unix/af_unix.c:2708 net/unix/af_unix.c:2847) >> > > > unix_stream_recvmsg (net/unix/af_unix.c:3048) >> > > > sock_recvmsg (net/socket.c:1063 (discriminator 20) net/socket.c:1085 (discriminator 20)) >> > > > __sys_recvfrom (net/socket.c:2278) >> > > > __x64_sys_recvfrom (net/socket.c:2291 (discriminator 1) net/socket.c:2287 (discriminator 1) net/socket.c:2287 (discriminator 1)) >> > > > do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1)) >> > > > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) >> > > > RIP: 0033:0x7f8911fcea06 >> > > > Code: 5d e8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 75 19 83 e2 39 83 fa 08 75 11 e8 26 ff ff ff 66 0f 1f 44 00 00 48 8b 45 10 0f 05 <48> 8b 5d f8 c9 c3 0f 1f 40 00 f3 0f 1e fa 55 48 89 e5 48 83 ec 08 >> > > > RSP: 002b:00007fffdb0dccb0 EFLAGS: 00000202 ORIG_RAX: 000000000000002d >> > > > RAX: ffffffffffffffda RBX: 00007fffdb0dcdc8 RCX: 00007f8911fcea06 >> > > > RDX: 0000000000000001 RSI: 00007f8911a5e060 RDI: 0000000000000006 >> > > > RBP: 00007fffdb0dccd0 R08: 0000000000000000 R09: 0000000000000000 >> > > > R10: 0000000000000001 R11: 0000000000000202 R12: 00007f89119a7d20 >> > > > R13: ffffffffc4653600 R14: 0000000000000000 R15: 0000000000000000 >> > > > >> > > > >> > > > Allocated by task 315: >> > > > kasan_save_stack (mm/kasan/common.c:48) >> > > > kasan_save_track (mm/kasan/common.c:60 (discriminator 1) mm/kasan/common.c:69 (discriminator 1)) >> > > > __kasan_slab_alloc (mm/kasan/common.c:348) >> > > > kmem_cache_alloc_node_noprof (./include/linux/kasan.h:250 mm/slub.c:4148 mm/slub.c:4197 mm/slub.c:4249) >> > > > __alloc_skb (net/core/skbuff.c:660 (discriminator 4)) >> > > > alloc_skb_with_frags (./include/linux/skbuff.h:1336 net/core/skbuff.c:6668) >> > > > sock_alloc_send_pskb (net/core/sock.c:2993) >> > > > unix_stream_sendmsg (./include/net/sock.h:1847 net/unix/af_unix.c:2256 net/unix/af_unix.c:2418) >> > > > __sys_sendto (net/socket.c:712 (discriminator 20) net/socket.c:727 (discriminator 20) net/socket.c:2226 (discriminator 20)) >> > > > __x64_sys_sendto (net/socket.c:2233 (discriminator 1) net/socket.c:2229 (discriminator 1) net/socket.c:2229 (discriminator 1)) >> > > > do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1)) >> > > > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) >> > > > >> > > > Freed by task 315: >> > > > kasan_save_stack (mm/kasan/common.c:48) >> > > > kasan_save_track (mm/kasan/common.c:60 (discriminator 1) mm/kasan/common.c:69 (discriminator 1)) >> > > > kasan_save_free_info (mm/kasan/generic.c:579 (discriminator 1)) >> > > > __kasan_slab_free (mm/kasan/common.c:271) >> > > > kmem_cache_free (mm/slub.c:4643 (discriminator 3) mm/slub.c:4745 (discriminator 3)) >> > > > unix_stream_read_generic (net/unix/af_unix.c:3010) >> > > > unix_stream_recvmsg (net/unix/af_unix.c:3048) >> > > > sock_recvmsg (net/socket.c:1063 (discriminator 20) net/socket.c:1085 (discriminator 20)) >> > > > __sys_recvfrom (net/socket.c:2278) >> > > > __x64_sys_recvfrom (net/socket.c:2291 (discriminator 1) net/socket.c:2287 (discriminator 1) net/socket.c:2287 (discriminator 1)) >> > > > do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1)) >> > > > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) >> > > > >> > > > The buggy address belongs to the object at ffff888106ef28c0 >> > > > which belongs to the cache skbuff_head_cache of size 224 >> > > > The buggy address is located 68 bytes inside of >> > > > freed 224-byte region [ffff888106ef28c0, ffff888106ef29a0) >> > > > >> > > > The buggy address belongs to the physical page: >> > > > page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888106ef3cc0 pfn:0x106ef2 >> > > > head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 >> > > > flags: 0x200000000000040(head|node=0|zone=2) >> > > > page_type: f5(slab) >> > > > raw: 0200000000000040 ffff8881001d28c0 ffffea000422fe00 0000000000000004 >> > > > raw: ffff888106ef3cc0 0000000080190010 00000000f5000000 0000000000000000 >> > > > head: 0200000000000040 ffff8881001d28c0 ffffea000422fe00 0000000000000004 >> > > > head: ffff888106ef3cc0 0000000080190010 00000000f5000000 0000000000000000 >> > > > head: 0200000000000001 ffffea00041bbc81 00000000ffffffff 00000000ffffffff >> > > > head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 >> > > > page dumped because: kasan: bad access detected >> > > > >> > > > Memory state around the buggy address: >> > > > ffff888106ef2800: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc >> > > > ffff888106ef2880: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb >> > > > >ffff888106ef2900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >> > > > ^ >> > > > ffff888106ef2980: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc >> > > > ffff888106ef2a00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >> > > > >> > > > Fixes: 314001f0bf92 ("af_unix: Add OOB support") >> > > >> > > Do we know why this stopped at v6.1? >> > > >> > > The Fixes: commit was added in v5.15 and this appears to apply fine. >> > > >> > > If it helps, the upstream commit was: >> > > >> > > 32ca245464e1 af_unix: Don't leave consecutive consumed OOB skbs. >> > >> > Commits that are not explicitly tagged with "cc: stable@" are not always >> > backported everywhere. They are done on a "hey, let's run a script and >> > see what falls out" type of method as the maintainer and developer >> > involved didn't explicitly ask for it to be applied. >> >> Right. I'm just surprised that it was backported to some branches, but >> not others, despite seemingly applying just fine and the Fixes: tag >> indicating that it should be applied to v5.15 as well. >> >> > If you think it should be added to other branches, please always let us >> > know and ideally, send a working backport :) >> >> I just did let you know. :) >> >> No backport required. It should just apply. > >I applied it again and submitted it for build testing. > >Once complete, I'll let you know the result. At least on my end there's a big scary build error when I try this on 5.15 :) -- Thanks, Sasha