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Sat, 31 Oct 2026 09:51:20 -0700 (PDT) Date: Sat, 31 Oct 2026 09:51:20 -0700 X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6ae61c88.6552420f.2a0efc.0003.GAE@google.com> Subject: [syzbot] [netfilter?] WARNING in nf_flow_offload_gc_step From: syzbot To: coreteam@netfilter.org, davem@davemloft.net, edumazet@kernel.org, fw@strlen.de, horms@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, pabeni@redhat.com, pablo@netfilter.org, phil@nwl.cc, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" Hello, syzbot found the following issue on: HEAD commit: d135ab453a74 Merge tag 'backlight-next-7.4' of git://git.k.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=13a51259580000 kernel config: https://syzkaller.appspot.com/x/.config?x=6f2905533069b0f5 dashboard link: https://syzkaller.appspot.com/bug?extid=e1a88d8b7e4cf6b51d85 compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14020995580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=100c4f0d580000 Downloadable assets: disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-d135ab45.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/6c39e8158fba/vmlinux-d135ab45.xz kernel image: https://storage.googleapis.com/syzbot-assets/7fb9f97c1f88/bzImage-d135ab45.xz AI-generated root cause summary: In the Netfilter flowtable subsystem, nf_flow_table_extend_ct_timeout() only accounts for IPPROTO_UDP and IPPROTO_TCP when refreshing conntrack timeouts during garbage collection. However, both tc act_ct and nftables flow offload support offloading IPPROTO_GRE connections to the flowtable. When the garbage collector checks an offloaded GRE connection whose timeout has dropped below min_timeout, the missing case in nf_flow_table_extend_ct_timeout() triggers the default: WARN_ON_ONCE(1) branch. In a production kernel without panic_on_warn, the warning does not crash the system and no memory corruption occurs. full analysis: https://syzkaller.appspot.com/x/ai_root_cause?x=e1a88d8b7e4cf6b51d85 IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+e1a88d8b7e4cf6b51d85@syzkaller.appspotmail.com ------------[ cut here ]------------ 1 WARNING: net/netfilter/nf_flow_table_core.c:553 at nf_flow_table_extend_ct_timeout net/netfilter/nf_flow_table_core.c:553 [inline], CPU#2: kworker/2:2/1358 WARNING: net/netfilter/nf_flow_table_core.c:553 at nf_flow_offload_gc_step+0xd84/0xf60 net/netfilter/nf_flow_table_core.c:593, CPU#2: kworker/2:2/1358 Modules linked in: CPU: 2 UID: 0 PID: 1358 Comm: kworker/2:2 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: events_power_efficient nf_flow_offload_work_gc RIP: 0010:nf_flow_table_extend_ct_timeout net/netfilter/nf_flow_table_core.c:553 [inline] RIP: 0010:nf_flow_offload_gc_step+0xd84/0xf60 net/netfilter/nf_flow_table_core.c:593 Code: f8 e9 82 fd ff ff 4c 89 f7 e8 28 e1 6a f8 e9 12 fc ff ff 48 c7 c7 80 f2 c0 8f e8 17 e1 6a f8 e9 ae fc ff ff e8 1d cb f1 f7 90 <0f> 0b 90 41 be 01 00 00 00 e9 7d fc ff ff e8 09 cb f1 f7 48 8b 04 RSP: 0018:ffffc9000618fa88 EFLAGS: 00010293 RAX: 0000000000000000 RBX: ffff88803e161380 RCX: 0000000000000000 RDX: ffff88802c392580 RSI: ffffffff8a1c51f3 RDI: ffff88802c392580 RBP: ffff88803e161488 R08: 0000000000000001 R09: 0000000000000011 R10: 000000000000002f R11: 0000000000000000 R12: 1ffff92000c31f56 R13: ffff88803818f868 R14: 000000000000002f R15: ffffffff8fc0f280 FS: 0000000000000000(0000) GS:ffff8880d469c000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000200000012000 CR3: 000000002f277000 CR4: 0000000000352ef0 Call Trace: nf_flow_table_iterate net/netfilter/nf_flow_table_core.c:459 [inline] nf_flow_table_gc_run net/netfilter/nf_flow_table_core.c:616 [inline] nf_flow_offload_work_gc+0x11e/0x1e0 net/netfilter/nf_flow_table_core.c:624 process_one_work+0xac7/0x1b10 kernel/workqueue.c:3495 process_scheduled_works kernel/workqueue.c:3578 [inline] worker_thread+0x5ef/0xe50 kernel/workqueue.c:3659 kthread+0x373/0x450 kernel/kthread.c:436 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 --- This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at syzkaller@googlegroups.com. syzbot will keep track of this issue. See: https://goo.gl/tpsmEJ#status for how to communicate with syzbot. If the report is already addressed, let syzbot know by replying with: #syz fix: exact-commit-title 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. If you want to overwrite report's subsystems, reply with: #syz set subsystems: new-subsystem (See the list of subsystem names on the web dashboard) If the report is a duplicate of another one, reply with: #syz dup: exact-subject-of-another-report If you want to undo deduplication, reply with: #syz undup