syzbot


WARNING in em_nbyte_match

Status: upstream: reported C repro on 2025/11/21 15:29
Subsystems: net
[Documentation on labels]
Reported-by: syzbot+f3a497f02c389d86ef16@syzkaller.appspotmail.com
Fix commit: 4fe5a00ec707 net: sched: fix TCF_LAYER_TRANSPORT handling in tcf_get_base_ptr()
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-kmsan-gce-386-root ci-upstream-kmsan-gce-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]
First crash: 20d, last: 5d08h
Cause bisection: introduced by (bisect log) :
commit 66e4c8d950083df8e12981babca788e1635c92b6
Author: Eric Dumazet <edumazet@google.com>
Date: Tue May 10 03:57:39 2022 +0000

  net: warn if transport header was not set

Crash: WARNING in em_nbyte_match (log)
Repro: C syz .config
  
Discussions (2)
Title Replies (including bot) Last reply
[PATCH net-next] net: sched: fix TCF_LAYER_TRANSPORT handling in tcf_get_base_ptr() 3 (3) 2025/11/25 03:10
[syzbot] [net?] WARNING in em_nbyte_match 0 (2) 2025/11/22 01:17
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 WARNING in em_nbyte_match origin:lts-only -1 C 3 4d14h 5d08h 0/2 upstream: reported C repro on 2025/12/06 11:58
linux-6.1 WARNING in em_nbyte_match origin:lts-only -1 C 9 2d17h 5d08h 0/3 upstream: reported C repro on 2025/12/06 11:53
Last patch testing requests (1)
Created Duration User Patch Repo Result
2025/11/21 14:00 29m edumazet@google.com patch net OK log

Sample crash report:
syzkaller0: entered promiscuous mode
syzkaller0: entered allmulticast mode
------------[ cut here ]------------
WARNING: CPU: 0 PID: 6013 at ./include/linux/skbuff.h:3071 skb_transport_header include/linux/skbuff.h:3071 [inline]
WARNING: CPU: 0 PID: 6013 at ./include/linux/skbuff.h:3071 tcf_get_base_ptr include/net/pkt_cls.h:539 [inline]
WARNING: CPU: 0 PID: 6013 at ./include/linux/skbuff.h:3071 em_nbyte_match+0x2d8/0x3f0 net/sched/em_nbyte.c:43
Modules linked in:
CPU: 0 UID: 0 PID: 6013 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:skb_transport_header include/linux/skbuff.h:3071 [inline]
RIP: 0010:tcf_get_base_ptr include/net/pkt_cls.h:539 [inline]
RIP: 0010:em_nbyte_match+0x2d8/0x3f0 net/sched/em_nbyte.c:43
Code: 31 c0 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d e9 8d 08 e4 01 cc e8 a7 a7 5a f8 90 0f 0b 90 e9 de fe ff ff e8 99 a7 5a f8 90 <0f> 0b 90 e9 f7 fd ff ff 89 d1 80 e1 07 fe c1 38 c1 0f 8c 71 fd ff
RSP: 0018:ffffc900038fefd8 EFLAGS: 00010293
RAX: ffffffff89655c27 RBX: ffff88803039f3c0 RCX: ffff88802f1d0000
RDX: 0000000000000000 RSI: 000000000000ffff RDI: 000000000000ffff
RBP: 000000000000ffff R08: ffff88802f1d0000 R09: 0000000000000003
R10: 0000000000000002 R11: 0000000000000000 R12: dffffc0000000000
R13: 1ffff11006073e8e R14: ffff8880301e5580 R15: 1ffff1100603cab0
FS:  00005555576be500(0000) GS:ffff88812613b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000002280 CR3: 0000000062390000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 tcf_em_match net/sched/ematch.c:494 [inline]
 __tcf_em_tree_match+0x1ac/0x770 net/sched/ematch.c:520
 tcf_em_tree_match include/net/pkt_cls.h:512 [inline]
 basic_classify+0x115/0x2d0 net/sched/cls_basic.c:50
 tc_classify include/net/tc_wrapper.h:197 [inline]
 __tcf_classify net/sched/cls_api.c:1764 [inline]
 tcf_classify+0x4cf/0x1140 net/sched/cls_api.c:1860
 multiq_classify net/sched/sch_multiq.c:39 [inline]
 multiq_enqueue+0xfd/0x4c0 net/sched/sch_multiq.c:66
 dev_qdisc_enqueue+0x4e/0x260 net/core/dev.c:4118
 __dev_xmit_skb net/core/dev.c:4214 [inline]
 __dev_queue_xmit+0xe83/0x3b50 net/core/dev.c:4729
 packet_snd net/packet/af_packet.c:3076 [inline]
 packet_sendmsg+0x3e33/0x5080 net/packet/af_packet.c:3108
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 ____sys_sendmsg+0x505/0x830 net/socket.c:2630
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
 __sys_sendmsg net/socket.c:2716 [inline]
 __do_sys_sendmsg net/socket.c:2721 [inline]
 __se_sys_sendmsg net/socket.c:2719 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f02b7d8f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffef050ec08 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f02b7fe5fa0 RCX: 00007f02b7d8f749
RDX: 0000000000000004 RSI: 00002000000000c0 RDI: 0000000000000007
RBP: 00007f02b7e13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f02b7fe5fa0 R14: 00007f02b7fe5fa0 R15: 0000000000000003
 </TASK>

Crashes (7):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/21 12:38 net 8e621c9a3375 280ea308 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING in em_nbyte_match
2025/11/21 08:52 net 8e621c9a3375 280ea308 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING in em_nbyte_match
2025/11/21 07:12 net 8e621c9a3375 280ea308 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING in em_nbyte_match
2025/11/21 05:22 net 8e621c9a3375 280ea308 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING in em_nbyte_match
2025/11/21 03:32 net 8e621c9a3375 280ea308 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce WARNING in em_nbyte_match
2025/12/06 11:50 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 05c93f3395ed d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in em_nbyte_match
2025/12/06 11:50 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 05c93f3395ed d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in em_nbyte_match
* Struck through repros no longer work on HEAD.