WARNING in __skb_flow_dissect (8)

Status: upstream: reported C repro on 2026/09/28 19:41
Subsystems: net
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+9408fbe0e6452a12e9ab@syzkaller.appspotmail.com
Fix commit: 8ec454dcd00c ipv6: sr: use skb_get_hash_net() in seg6_make_flowlabel()
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-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce 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-qemu2-riscv64 ci-upstream-gce-arm64 ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root]
First crash: 8d22h, last: 8d18h
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
68a4f06e assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ WARNING in __skb_flow_dissect (8) 2026/09/28 05:55 2026/09/28 05:55 2026/09/28 05:59 a3c7249d
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH net] ipv6: sr: use skb_get_hash_net() in seg6_make_flowlabel() 4 (4) 2026/10/01 01:00
[syzbot] [net?] WARNING in __skb_flow_dissect (8) 0 (1) 2026/09/28 19:41
▶ ▼ Similar bugs (8)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in __skb_flow_dissect (6) net -1 1 881d 881d 27/29 fixed on 2024/08/14 19:57
linux-6.1 WARNING in __skb_flow_dissect origin:lts-only -1 syz, C error 156 2d00h 261d 0/3 upstream: reported C repro on 2026/01/17 07:47
upstream WARNING in __skb_flow_dissect net -1 syz 3 2917d 2918d 11/29 fixed on 2018/10/11 18:37
upstream WARNING in __skb_flow_dissect (5) net -1 1 921d 921d 0/29 closed as invalid on 2024/04/26 11:59
upstream WARNING in __skb_flow_dissect (7) net -1 275 265d 258d 29/29 fixed on 2026/05/06 16:40
linux-6.6 WARNING in __skb_flow_dissect origin:lts-only -1 syz, C 73 3d18h 175d 0/2 upstream: reported C repro on 2026/04/13 06:50
upstream WARNING in __skb_flow_dissect (3) net -1 syz 224 2820d 2909d 11/29 fixed on 2019/03/06 07:43
upstream WARNING in __skb_flow_dissect (4) net -1 syz, C error 6 1430d 1439d 22/29 fixed on 2023/02/24 13:50
▶ ▼ Last patch testing requests (1)
Created Duration User Patch Repo Result
2026/09/28 19:18 1h52m edumazet@google.com patch git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci OK job log log

Sample crash report:
tipc: Started in network mode
tipc: Node identity ac14143b, cluster identity 4711
tipc: New replicast peer: 10.1.1.0
------------[ cut here ]------------
WARNING: net/core/flow_dissector.c:1131 at __skb_flow_dissect+0x910/0x5368 net/core/flow_dissector.c:1126, CPU#1: syz.0.17/4912
Modules linked in:
CPU: 1 UID: 0 PID: 4912 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __skb_flow_dissect+0x910/0x5368 net/core/flow_dissector.c:1126
lr : __skb_flow_dissect+0x910/0x5368 net/core/flow_dissector.c:1126
sp : ffff800094906200
x29: ffff800094906700 x28: 0000000000000000 x27: 0000000000000002
x26: 0000000000000000 x25: ffff0000d05fd3c0 x24: dfff800000000000
x23: 0000000000000000 x22: 1ffff0001114beb7 x21: ffff800088a5f5b0
x20: 0000000000000000 x19: ffff700012920c58 x18: 00000000ffffffff
x17: ffff8000863d2120 x16: ffff8000863d32f4 x15: ffff80008a707000
x14: 000000000064059a x13: 0000000000000009 x12: 0000000000000009
x11: 00000000d6794b26 x10: 0000000000000003 x9 : 0000000000000400
x8 : 0000000000000000 x7 : ffff800084c05fcc x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff800084c05fe8
x2 : 0000000000000001 x1 : ffff0000c46c9d80 x0 : 0000000000000000
Call trace:
 __skb_flow_dissect+0x910/0x5368 net/core/flow_dissector.c:1126 (P)
 __skb_get_hash_net+0xe0/0x29c net/core/flow_dissector.c:1903
 skb_get_hash include/linux/skbuff.h:1663 [inline]
 seg6_make_flowlabel+0xcc/0x1ec net/ipv6/seg6_iptunnel.c:132
 __seg6_do_srh_encap+0x320/0xbf4 net/ipv6/seg6_iptunnel.c:161
 seg6_do_srh+0x4b4/0xa44 net/ipv6/seg6_iptunnel.c:431
 seg6_output_core+0x164/0x688 net/ipv6/seg6_iptunnel.c:681
 seg6_output+0x44/0x1ac net/ipv6/seg6_iptunnel.c:744
 lwtunnel_output+0x3d0/0x664 net/core/lwtunnel.c:356
 dst_output include/net/dst.h:470 [inline]
 ip_local_out+0x110/0x148 net/ipv4/ip_output.c:131
 iptunnel_xmit+0x50c/0xd38 net/ipv4/ip_tunnel_core.c:97
 udp_tunnel_xmit_skb+0x220/0x348 net/ipv4/udp_tunnel_core.c:187
 tipc_udp_xmit+0x75c/0x9c0 net/tipc/udp_media.c:202
 tipc_udp_send_msg+0x214/0x374 net/tipc/udp_media.c:274
 tipc_bearer_xmit_skb+0x260/0x3b0 net/tipc/bearer.c:576
 tipc_enable_bearer net/tipc/bearer.c:366 [inline]
 __tipc_nl_bearer_enable+0xc90/0xfb0 net/tipc/bearer.c:1048
 tipc_nl_bearer_enable+0x2c/0x48 net/tipc/bearer.c:1057
 genl_family_rcv_msg_doit+0x1e4/0x2d4 net/netlink/genetlink.c:1114
 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
 genl_rcv_msg+0x43c/0x620 net/netlink/genetlink.c:1209
 netlink_rcv_skb+0x238/0x414 net/netlink/af_netlink.c:2575
 genl_rcv+0x38/0x50 net/netlink/genetlink.c:1218
 netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
 netlink_unicast+0x600/0x7f8 net/netlink/af_netlink.c:1364
 netlink_sendmsg+0x648/0x948 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:800 [inline]
 __sock_sendmsg+0xc8/0x17c net/socket.c:815
 ____sys_sendmsg+0x3d0/0x6c8 net/socket.c:2713
 ___sys_sendmsg+0x198/0x224 net/socket.c:2767
 __sys_sendmsg+0x158/0x204 net/socket.c:2799
 __do_sys_sendmsg net/socket.c:2804 [inline]
 __se_sys_sendmsg net/socket.c:2802 [inline]
 __arm64_sys_sendmsg+0x88/0x9c net/socket.c:2802
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
irq event stamp: 1573
hardirqs last  enabled at (1572): [<ffff80008030a2b4>] __local_bh_enable_ip+0x14c/0x234 kernel/softirq.c:478
hardirqs last disabled at (1573): [<ffff80008685dbf4>] el1_brk64+0x20/0x54 arch/arm64/kernel/entry-common.c:483
softirqs last  enabled at (1546): [<ffff800084bb85e4>] __alloc_skb+0x1c0/0x610 net/core/skbuff.c:698
softirqs last disabled at (1552): [<ffff8000863d31fc>] local_bh_disable include/linux/bottom_half.h:20 [inline]
softirqs last disabled at (1552): [<ffff8000863d31fc>] tipc_udp_xmit+0xb8/0x9c0 net/tipc/udp_media.c:181
---[ end trace 0000000000000000 ]---
tipc: Enabled bearer <udp:syz1>, priority 10

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/27 04:08 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci e8e60d3ddd25 a3c7249d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in __skb_flow_dissect
2026/09/27 03:21 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci e8e60d3ddd25 a3c7249d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in __skb_flow_dissect
2026/09/27 02:33 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci e8e60d3ddd25 a3c7249d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in __skb_flow_dissect
2026/09/27 01:43 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci e8e60d3ddd25 a3c7249d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in __skb_flow_dissect
2026/09/27 00:55 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci e8e60d3ddd25 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in __skb_flow_dissect
* Struck through repros no longer work on HEAD.