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 D4ACC35C1B8; Fri, 9 Jan 2026 12:48:34 +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=1767962914; cv=none; b=LR6RVeUnPy/cokJSl5hjXB5KDx5LjRCZArZQgulTyan0HUe1uX6TIyCdlIs8uIPgOz6eiARS5FfEQb3EfMKDyVCIaeKle7RLANma5zw6kZ3wC+qwrFfxd0tvxzZv6p/924OndjJjMplui3WnDXVSjKiBkFB62/7/E0+zZmT0tto= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767962914; c=relaxed/simple; bh=+g+jK7t85J9CvAXSuvZ+BausVgKBimPP8fhZ0FXKcQg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mCM4o6ttR0WeeMpR04a8QXRovQg5DZr+H7/Q5KkZHjQrIcIBTAOcX3qJqjj0e9Lj+ROtGXKghpn/9T5wxmUkCluG3dDaTOvCUHDmQeqcfJ1mFJ/MTX3fi7KMK0cc/JyjehhiqTDi0iJN+zf9SZbh+3xbTSoaq+pDtFEX9d7zYyk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dI5BOaTz; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="dI5BOaTz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30AFFC4CEF1; Fri, 9 Jan 2026 12:48:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767962914; bh=+g+jK7t85J9CvAXSuvZ+BausVgKBimPP8fhZ0FXKcQg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dI5BOaTz5WHCg17d/g9ltFG8Ch0CpkfF+pRrxAdJbaJEk+lwDErz1lKXw10bHVABi 4s+eKW+5UsIv6ipjjarFTDXKuewQbjtKmwwIuUMuJ809jwdwTeJ5aMdrsoPiyBUelH GZ9tbfjDZAw7/HJN6ZHVbLeTK2N0MSe7pSW2yFb0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+3a92d359bc2ec6255a33@syzkaller.appspotmail.com, Kuniyuki Iwashima , "Matthieu Baerts (NGI0)" , Paolo Abeni , Sasha Levin Subject: [PATCH 6.1 533/634] mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose(). Date: Fri, 9 Jan 2026 12:43:31 +0100 Message-ID: <20260109112137.628030316@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260109112117.407257400@linuxfoundation.org> References: <20260109112117.407257400@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kuniyuki Iwashima [ Upstream commit f07f4ea53e22429c84b20832fa098b5ecc0d4e35 ] syzbot reported divide-by-zero in __tcp_select_window() by MPTCP socket. [0] We had a similar issue for the bare TCP and fixed in commit 499350a5a6e7 ("tcp: initialize rcv_mss to TCP_MIN_MSS instead of 0"). Let's apply the same fix to mptcp_do_fastclose(). [0]: Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 0 UID: 0 PID: 6068 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:__tcp_select_window+0x824/0x1320 net/ipv4/tcp_output.c:3336 Code: ff ff ff 44 89 f1 d3 e0 89 c1 f7 d1 41 01 cc 41 21 c4 e9 a9 00 00 00 e8 ca 49 01 f8 e9 9c 00 00 00 e8 c0 49 01 f8 44 89 e0 99 7c 24 1c 41 29 d4 48 bb 00 00 00 00 00 fc ff df e9 80 00 00 00 RSP: 0018:ffffc90003017640 EFLAGS: 00010293 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88807b469e40 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffc90003017730 R08: ffff888033268143 R09: 1ffff1100664d028 R10: dffffc0000000000 R11: ffffed100664d029 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 000055557faa0500(0000) GS:ffff888126135000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f64a1912ff8 CR3: 0000000072122000 CR4: 00000000003526f0 Call Trace: tcp_select_window net/ipv4/tcp_output.c:281 [inline] __tcp_transmit_skb+0xbc7/0x3aa0 net/ipv4/tcp_output.c:1568 tcp_transmit_skb net/ipv4/tcp_output.c:1649 [inline] tcp_send_active_reset+0x2d1/0x5b0 net/ipv4/tcp_output.c:3836 mptcp_do_fastclose+0x27e/0x380 net/mptcp/protocol.c:2793 mptcp_disconnect+0x238/0x710 net/mptcp/protocol.c:3253 mptcp_sendmsg_fastopen+0x2f8/0x580 net/mptcp/protocol.c:1776 mptcp_sendmsg+0x1774/0x1980 net/mptcp/protocol.c:1855 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0xe5/0x270 net/socket.c:742 __sys_sendto+0x3bd/0x520 net/socket.c:2244 __do_sys_sendto net/socket.c:2251 [inline] __se_sys_sendto net/socket.c:2247 [inline] __x64_sys_sendto+0xde/0x100 net/socket.c:2247 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f66e998f749 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffff9acedb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00007f66e9be5fa0 RCX: 00007f66e998f749 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003 RBP: 00007ffff9acee10 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 00007f66e9be5fa0 R14: 00007f66e9be5fa0 R15: 0000000000000006 Fixes: ae155060247b ("mptcp: fix duplicate reset on fastclose") Reported-by: syzbot+3a92d359bc2ec6255a33@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/69260882.a70a0220.d98e3.00b4.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima Reviewed-by: Matthieu Baerts (NGI0) Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20251125195331.309558-1-kuniyu@google.com Signed-off-by: Paolo Abeni [ Adjust context ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- net/mptcp/protocol.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -2806,6 +2806,12 @@ static void mptcp_do_fastclose(struct so goto unlock; subflow->send_fastclose = 1; + + /* Initialize rcv_mss to TCP_MIN_MSS to avoid division by 0 + * issue in __tcp_select_window(), see tcp_disconnect(). + */ + inet_csk(ssk)->icsk_ack.rcv_mss = TCP_MIN_MSS; + tcp_send_active_reset(ssk, ssk->sk_allocation); unlock: release_sock(ssk);