syzbot


WARNING in __skb_flow_dissect

Status: upstream: reported C repro on 2026/04/13 06:50
Reported-by: syzbot+0a444a911c34d9b5ca5c@syzkaller.appspotmail.com
First crash: 18d, last: 4h52m
Similar bugs (7)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in __skb_flow_dissect (6) net -1 1 724d 724d 27/29 fixed on 2024/08/14 19:57
linux-6.1 WARNING in __skb_flow_dissect -1 C 20 13d 104d 0/3 upstream: reported C repro on 2026/01/17 07:47
upstream WARNING in __skb_flow_dissect net -1 syz 3 2760d 2761d 11/29 fixed on 2018/10/11 18:37
upstream WARNING in __skb_flow_dissect (5) net -1 1 764d 764d 0/29 closed as invalid on 2024/04/26 11:59
upstream WARNING in __skb_flow_dissect (7) net -1 275 108d 101d 28/29 upstream: reported on 2026/01/20 16:15
upstream WARNING in __skb_flow_dissect (3) net -1 syz 224 2663d 2753d 11/29 fixed on 2019/03/06 07:43
upstream WARNING in __skb_flow_dissect (4) net -1 C error 6 1273d 1282d 22/29 fixed on 2023/02/24 13:50

Sample crash report:
------------[ cut here ]------------
WARNING: CPU: 1 PID: 5945 at net/core/flow_dissector.c:1107 __skb_flow_dissect+0xbde/0x6d60 net/core/flow_dissector.c:1102
Modules linked in:
CPU: 1 PID: 5945 Comm: syz.0.36 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:__skb_flow_dissect+0xbde/0x6d60 net/core/flow_dissector.c:1107
Code: db 59 00 00 80 3d 70 ac fd 05 01 0f 85 01 5a 00 00 e8 06 27 0f f9 e9 17 f9 ff ff e8 fc 26 0f f9 e9 b4 03 00 00 e8 f2 26 0f f9 <0f> 0b e9 00 ff ff ff e8 e6 26 0f f9 c6 05 3b ac fd 05 01 48 c7 c7
RSP: 0018:ffffc900001ef980 EFLAGS: 00010246
RAX: ffffffff8877fb0e RBX: ffff88807c290870 RCX: ffff8880308dbc00
RDX: 0000000000000100 RSI: ffffffff8b1c8f80 RDI: ffffffff8b1c8f40
RBP: ffffc900001eff98 R08: dffffc0000000000 R09: 1ffffffff2238ca0
R10: dffffc0000000000 R11: fffffbfff2238ca1 R12: ffffffff8e8b8b78
R13: ffffffff8877f129 R14: 0000000000000000 R15: 1ffffffff1d17170
FS:  0000555574737500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffa5f672700 CR3: 000000007285a000 CR4: 00000000003506e0
Call Trace:
 <IRQ>
 skb_flow_dissect_flow_keys include/linux/skbuff.h:1544 [inline]
 ___skb_get_hash net/core/flow_dissector.c:1801 [inline]
 __skb_get_hash+0xf3/0x2e0 net/core/flow_dissector.c:1866
 skb_get_hash include/linux/skbuff.h:1586 [inline]
 nft_trace_init+0x1bb/0x410 net/netfilter/nf_tables_trace.c:316
 nft_do_chain+0x14fc/0x1600 net/netfilter/nf_tables_core.c:268
 nf_route_table_hook6+0x366/0x7b0 net/netfilter/nft_chain_route.c:88
 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline]
 nf_hook_slow+0xbd/0x200 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:259 [inline]
 __ip6_local_out+0x784/0x8a0 net/ipv6/output_core.c:143
 ip6_local_out+0x2a/0x130 net/ipv6/output_core.c:153
 ip6tunnel_xmit include/net/ip6_tunnel.h:161 [inline]
 udp_tunnel6_xmit_skb+0x53e/0x970 net/ipv6/ip6_udp_tunnel.c:109
 tipc_udp_xmit+0x58d/0xb40 net/tipc/udp_media.c:220
 tipc_bearer_xmit_skb+0x2ad/0x3f0 net/tipc/bearer.c:575
 tipc_disc_timeout+0x596/0x6f0 net/tipc/discover.c:338
 call_timer_fn+0x189/0x540 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x542/0x800 kernel/time/timer.c:2023
 run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xd3/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:__orc_find arch/x86/kernel/unwind_orc.c:99 [inline]
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:227 [inline]
RIP: 0010:unwind_next_frame+0x4cf/0x2970 arch/x86/kernel/unwind_orc.c:494
Code: 75 3e 4d 63 2f 4d 01 fd 4c 89 ef 4c 89 f6 e8 98 e7 4b 00 49 8d 47 04 4d 39 f5 4c 0f 46 e0 49 8d 47 fc 48 0f 47 d8 49 0f 46 ef <49> 39 dc 77 28 e8 67 e5 4b 00 48 ba 00 00 00 00 00 fc ff df eb 97
RSP: 0018:ffffc900033e69b8 EFLAGS: 00000297
RAX: ffffffff8ef0a2d8 RBX: ffffffff8ef0a2e0 RCX: ffff8880308dbc00
RDX: 0000000000000000 RSI: ffffffff88b40ced RDI: ffffffff88b40cab
RBP: ffffffff8ef0a2dc R08: ffffc900033e6b50 R09: 0000000000000008
R10: 0000000000000004 R11: 0000000000000000 R12: ffffffff8ef0a2e0
R13: ffffffff88b40cab R14: ffffffff88b40ced R15: ffffffff8ef0a2dc
 arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xaa/0x100 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4b0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 kmem_cache_alloc_node+0x14c/0x320 mm/slub.c:3540
 kmalloc_reserve+0x95/0x240 net/core/skbuff.c:562
 pskb_expand_head+0x180/0x1190 net/core/skbuff.c:2100
 netlink_trim+0x180/0x220 net/netlink/af_netlink.c:1301
 netlink_unicast+0x66/0x8d0 net/netlink/af_netlink.c:1336
 nlmsg_unicast include/net/netlink.h:1107 [inline]
 nlmsg_notify+0x12e/0x1a0 net/netlink/af_netlink.c:2596
 nft_commit_notify net/netfilter/nf_tables_api.c:10134 [inline]
 nf_tables_commit+0x64ff/0x7c10 net/netfilter/nf_tables_api.c:10532
 nfnetlink_rcv_batch net/netfilter/nfnetlink.c:569 [inline]
 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:639 [inline]
 nfnetlink_rcv+0x1ad8/0x24a0 net/netfilter/nfnetlink.c:657
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x751/0x8d0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d0/0xbf0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x5ba/0x960 net/socket.c:2594
 ___sys_sendmsg+0x2a6/0x360 net/socket.c:2648
 __sys_sendmsg net/socket.c:2677 [inline]
 __do_sys_sendmsg net/socket.c:2686 [inline]
 __se_sys_sendmsg+0x1c2/0x2b0 net/socket.c:2684
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7ffa5f79cdd9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd8c1aca68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ffa5fa15fa0 RCX: 00007ffa5f79cdd9
RDX: 0000000000000000 RSI: 0000200000000000 RDI: 0000000000000005
RBP: 00007ffa5f832d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffa5fa15fac R14: 00007ffa5fa15fa0 R15: 00007ffa5fa15fa0
 </TASK>
----------------
Code disassembly (best guess):
   0:	75 3e                	jne    0x40
   2:	4d 63 2f             	movslq (%r15),%r13
   5:	4d 01 fd             	add    %r15,%r13
   8:	4c 89 ef             	mov    %r13,%rdi
   b:	4c 89 f6             	mov    %r14,%rsi
   e:	e8 98 e7 4b 00       	call   0x4be7ab
  13:	49 8d 47 04          	lea    0x4(%r15),%rax
  17:	4d 39 f5             	cmp    %r14,%r13
  1a:	4c 0f 46 e0          	cmovbe %rax,%r12
  1e:	49 8d 47 fc          	lea    -0x4(%r15),%rax
  22:	48 0f 47 d8          	cmova  %rax,%rbx
  26:	49 0f 46 ef          	cmovbe %r15,%rbp
* 2a:	49 39 dc             	cmp    %rbx,%r12 <-- trapping instruction
  2d:	77 28                	ja     0x57
  2f:	e8 67 e5 4b 00       	call   0x4be59b
  34:	48 ba 00 00 00 00 00 	movabs $0xdffffc0000000000,%rdx
  3b:	fc ff df
  3e:	eb 97                	jmp    0xffffffd7

Crashes (9):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/01 21:30 linux-6.6.y 258cf62a6dfd 753c55b9 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/05/01 07:09 linux-6.6.y 258cf62a6dfd 753c55b9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/05/01 07:08 linux-6.6.y 258cf62a6dfd 753c55b9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/04/30 01:44 linux-6.6.y 142cd8382222 005438fc .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/04/28 14:57 linux-6.6.y 142cd8382222 ce741359 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/04/25 05:06 linux-6.6.y 9760bf04666d 9c2d0995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/04/24 16:56 linux-6.6.y 9760bf04666d 1c2b9291 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/04/13 19:05 linux-6.6.y 8cee53b8eaeb 9530ccf9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
2026/04/13 06:49 linux-6.6.y 8cee53b8eaeb 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan WARNING in __skb_flow_dissect
* Struck through repros no longer work on HEAD.