FAILED: patch "[PATCH] mptcp: Initialise rcv_mss before calling" failed to apply to 6.1-stable tree

PATCH New [email protected] 2 participants 2 messages Dec 3, 2025 – Dec 8, 2025

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author maintainer

2025-12-03 13:34 UTC #0 lore raw

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x f07f4ea53e22429c84b20832fa098b5ecc0d4e35
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025120333-undamaged-punctual-31dc@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f07f4ea53e22429c84b20832fa098b5ecc0d4e35 Mon Sep 17 00:00:00 2001
From: Kuniyuki Iwashima <[email protected]>
Date: Tue, 25 Nov 2025 19:53:29 +0000
Subject: [PATCH] mptcp: Initialise rcv_mss before calling
tcp_send_active_reset() in mptcp_do_fastclose().

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 <f7> 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:
 <TASK>
 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
 </TASK>

Fixes ae155060247b ("mptcp: fix duplicate reset on fastclose")

Reported-by [email protected]

Closes https://lore.kernel.org/netdev/[email protected]/ open here

Signed-off-by Kuniyuki Iwashima <[email protected]>

Reviewed-by Matthieu Baerts (NGI0) <[email protected]>

Cc [email protected]

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Paolo Abeni <[email protected]>

net/mptcp/protocol.c +6 -0

index 8abb425d8b5f..1e413426deee 100644
@@ -2798,6 +2798,12 @@ static void mptcp_do_fastclose(struct sock *sk)
 			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,
 				      SK_RST_REASON_TCP_ABORT_ON_CLOSE);
 unlock:

Sasha Levin

maintainer

2025-12-08 13:00 UTC #1 lore raw

PATCH 1/1 mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose().

From: Kuniyuki Iwashima <[email protected]>

[ Upstream commit f07f4ea53e22429c84b20832fa098b5ecc0d4e35 ]