linux-kernel - Forwarded: Re: [syzbot] [mptcp?] WARNING in subflow_data

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Message-ID: <6927461c.a70a0220.d98e3.00df.GAE@google.com>
Date: Wed, 26 Nov 2025 10:25:32 -0800
From: syzbot <syzbot+0ff6b771b4f7a5bce83b@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org
Subject: Forwarded: Re: [syzbot] [mptcp?] WARNING in subflow_data_ready (4)

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Subject: Re: [syzbot] [mptcp?] WARNING in subflow_data_ready (4)
Author: pabeni@...hat.com

On 11/20/25 9:58 PM, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    8e621c9a3375 Merge tag 'net-6.18-rc7' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12887a12580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1cd7f786c0f5182f
> dashboard link: https://syzkaller.appspot.com/bug?extid=0ff6b771b4f7a5bce83b
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=133c9a12580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117a2a12580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/6be75789d60e/disk-8e621c9a.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/62e7a40cfe48/vmlinux-8e621c9a.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/3e523caa536d/bzImage-8e621c9a.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+0ff6b771b4f7a5bce83b@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 15 at net/mptcp/subflow.c:1519 subflow_data_ready+0x40b/0x7c0 net/mptcp/subflow.c:1519
> Modules linked in:
> CPU: 0 UID: 0 PID: 15 Comm: ksoftirqd/0 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> RIP: 0010:subflow_data_ready+0x40b/0x7c0 net/mptcp/subflow.c:1519
> Code: 89 ee e8 88 f8 72 f6 40 84 ed 75 21 e8 9e fd 72 f6 44 89 fe bf 07 00 00 00 e8 d1 f8 72 f6 41 83 ff 07 74 09 e8 86 fd 72 f6 90 <0f> 0b 90 e8 7d fd 72 f6 48 89 df e8 e5 ad ff ff 31 ff 89 c5 89 c6
> RSP: 0018:ffffc90000147380 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff888030aa72c0 RCX: ffffffff8b4959ef
> RDX: ffff88801d2cbc80 RSI: ffffffff8b4959fa RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000007
> R10: 0000000000000004 R11: 00000d230000000c R12: ffff888033463c00
> R13: 1ffff92000028e70 R14: ffff88802f9bbc00 R15: 0000000000000004
> FS:  0000000000000000(0000) GS:ffff888124a0d000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f841c04df98 CR3: 0000000078b7e000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  tcp_data_ready+0x110/0x550 net/ipv4/tcp_input.c:5355
>  tcp_data_queue+0x1aa6/0x5000 net/ipv4/tcp_input.c:5445
>  tcp_rcv_state_process+0xfb6/0x6490 net/ipv4/tcp_input.c:7159
>  tcp_v4_do_rcv+0x68e/0x10a0 net/ipv4/tcp_ipv4.c:1954
>  tcp_v4_rcv+0x3077/0x4db0 net/ipv4/tcp_ipv4.c:2374
>  ip_protocol_deliver_rcu+0xba/0x4c0 net/ipv4/ip_input.c:205
>  ip_local_deliver_finish+0x3f2/0x720 net/ipv4/ip_input.c:239
>  NF_HOOK include/linux/netfilter.h:318 [inline]
>  NF_HOOK include/linux/netfilter.h:312 [inline]
>  ip_local_deliver+0x18e/0x1f0 net/ipv4/ip_input.c:260
>  dst_input include/net/dst.h:474 [inline]
>  ip_rcv_finish net/ipv4/ip_input.c:453 [inline]
>  NF_HOOK include/linux/netfilter.h:318 [inline]
>  NF_HOOK include/linux/netfilter.h:312 [inline]
>  ip_rcv+0x2e0/0x600 net/ipv4/ip_input.c:573
>  __netif_receive_skb_one_core+0x197/0x1e0 net/core/dev.c:6079
>  __netif_receive_skb+0x1d/0x160 net/core/dev.c:6192
>  process_backlog+0x439/0x15e0 net/core/dev.c:6544
>  __napi_poll.constprop.0+0xba/0x550 net/core/dev.c:7594
>  napi_poll net/core/dev.c:7657 [inline]
>  net_rx_action+0x97f/0xef0 net/core/dev.c:7784
>  handle_softirqs+0x219/0x8e0 kernel/softirq.c:622
>  run_ksoftirqd kernel/softirq.c:1063 [inline]
>  run_ksoftirqd+0x3a/0x60 kernel/softirq.c:1055
>  smpboot_thread_fn+0x3f7/0xae0 kernel/smpboot.c:160
>  kthread+0x3c5/0x780 kernel/kthread.c:463
>  ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
> 
> 
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.

#syz test:
git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main

I can't repro it locally. Running a debug patch to collect more status
which hopefully should help understanding the race.