WARNING in tcf_ct_flow_table_process_conn

Status: upstream: reported C repro on 2026/09/12 23:39
Subsystems: net
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+6cc37aba98dac721c415@syzkaller.appspotmail.com
Fix commit: 47abe7a5c4eb net/sched: act_ct: don't WARN on benign flow_offload_alloc() failure
Patched on: [ci-qemu-gce-upstream-auto ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci-upstream-rust-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb], missing on: [ci-qemu-native-arm64-kvm ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root]
First crash: 42d, last: 23d
Cause bisection: failed (error log, bisect log)
  
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
90767030 repro-c Reproduced: ✅ ❓ WARNING in tcf_ct_flow_table_process_conn 2026/09/14 21:06 2026/09/14 21:06 2026/09/14 23:19 81a27d1a
b560dfda assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ❌ RemoteTrigger: ✅ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ✅ VMHostTrigger: ❌ ❓ WARNING in tcf_ct_flow_table_process_conn 2026/09/14 01:16 2026/09/14 01:16 2026/09/14 01:55 70a60e12
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH net] net/sched: act_ct: don't WARN on benign flow_offload_alloc() failure 3 (3) 2026/09/18 23:40
[syzbot] [net?] WARNING in tcf_ct_flow_table_process_conn 0 (2) 2026/09/17 08:16
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 WARNING in tcf_ct_flow_table_process_conn -1 syz, C 3 40d 40d 0/3 upstream: reported C repro on 2026/09/14 04:23
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/09/14 23:19 49m retest repro git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 704340f1cd0dcef829eb62f5b48ae95a2ce17bdf report job log log

Sample crash report:
RDX: 000000000000001c RSI: 0000200000000500 RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000000500
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
------------[ cut here ]------------
1
WARNING: net/sched/act_ct.c:437 at tcf_ct_flow_table_add net/sched/act_ct.c:437 [inline], CPU#0: syz-executor278/6366
WARNING: net/sched/act_ct.c:437 at tcf_ct_flow_table_process_conn+0x449/0x7c0 net/sched/act_ct.c:513, CPU#0: syz-executor278/6366
Modules linked in:
CPU: 0 UID: 0 PID: 6366 Comm: syz-executor278 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:tcf_ct_flow_table_add net/sched/act_ct.c:437 [inline]
RIP: 0010:tcf_ct_flow_table_process_conn+0x449/0x7c0 net/sched/act_ct.c:513
Code: 85 81 02 00 00 41 0f b7 2f 31 ff 89 ee e8 2f 67 e9 f7 85 ed 0f 84 7c 01 00 00 e8 e2 62 e9 f7 e9 e0 01 00 00 e8 d8 62 e9 f7 90 <0f> 0b 90 e9 b2 01 00 00 e8 ca 62 e9 f7 4d 89 f7 40 84 ed 74 27 e8
RSP: 0018:ffffc900042d6ef8 EFLAGS: 00010293
RAX: ffffffff89de6f88 RBX: ffff888070202000 RCX: ffff888028c90000
RDX: 0000000000000000 RSI: ffffffff8c6da060 RDI: ffffffff8c6da020
RBP: 0000000000000000 R08: 00000000ffffffff R09: 1ffffffff1dd5cfe
R10: dffffc0000000000 R11: fffffbfff1dd5cff R12: dffffc0000000000
R13: 1ffff1100e04041e R14: ffff8880702020c0 R15: 0000000000000001
FS:  000055556fc09400(0000) GS:ffff888124cd1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe25dff4c8 CR3: 0000000079ba6000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 tcf_ct_act+0x2a75/0x4050 net/sched/act_ct.c:1123
 tc_act include/net/tc_wrapper.h:131 [inline]
 tcf_action_exec+0x185/0x8d0 net/sched/act_api.c:1162
 tcf_exts_exec include/net/pkt_cls.h:361 [inline]
 basic_classify+0x1b2/0x2d0 net/sched/cls_basic.c:54
 tc_classify include/net/tc_wrapper.h:198 [inline]
 __tcf_classify net/sched/cls_api.c:1779 [inline]
 tcf_classify+0x43d/0x1160 net/sched/cls_api.c:1875
 tc_run+0x42d/0x750 net/core/dev.c:4463
 sch_handle_ingress net/core/dev.c:4538 [inline]
 __netif_receive_skb_core+0x1443/0x30c0 net/core/dev.c:6115
 __netif_receive_skb_one_core net/core/dev.c:6262 [inline]
 __netif_receive_skb net/core/dev.c:6377 [inline]
 netif_receive_skb_internal net/core/dev.c:6463 [inline]
 netif_receive_skb+0x1fe/0xbf0 net/core/dev.c:6522
 tun_rx_batched+0x1de/0x790 drivers/net/tun.c:1571
 tun_get_user+0x2be0/0x44d0 drivers/net/tun.c:2045
 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:2091
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6c0bc30879
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffff5b95668 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007ffff5b95690 RCX: 00007f6c0bc30879
RDX: 000000000000001c RSI: 0000200000000500 RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000000500
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Crashes (16):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/17 08:15 upstream 238650ef6c7c 95928915 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/22 14:58 upstream f0100363d8c3 e12281bd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/22 04:38 upstream f0100363d8c3 e12281bd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/17 06:38 upstream 238650ef6c7c 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/12 15:29 upstream 5225b8eec4c9 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/22 10:34 upstream 50d05c7c76c9 e12281bd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 WARNING in tcf_ct_flow_table_process_conn
2026/09/14 10:36 upstream 50d05c7c76c9 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 WARNING in tcf_ct_flow_table_process_conn
2026/09/22 22:08 upstream c4e9f74da438 3e2106e5 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in tcf_ct_flow_table_process_conn
2026/09/23 13:39 net-next 944ae66642b7 abce1216 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/22 14:50 net-next eabc76156e86 e12281bd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/22 12:21 net-next 2fba93180872 e12281bd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/09/12 23:40 net-next 879e280b8486 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce WARNING in tcf_ct_flow_table_process_conn
2026/10/01 02:30 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci e8e60d3ddd25 892a21ec .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in tcf_ct_flow_table_process_conn
2026/09/29 04:22 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci e8e60d3ddd25 7bf4ea23 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in tcf_ct_flow_table_process_conn
2026/09/23 22:22 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 7dc79bb50ab6 0a1606bc .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in tcf_ct_flow_table_process_conn
2026/09/22 14:55 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 38872197cae2 e12281bd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in tcf_ct_flow_table_process_conn
* Struck through repros no longer work on HEAD.