Subject: Re: [syzbot] [net?] general protection fault in ife_tlv_meta_encode

From: syzbot <[email-masked]>
Date: Wed, 21 Jan 2026 19:47:30 -0800

syzbot has found a reproducer for the following issue on:

HEAD commit:    d8f87aa5fa0a net: remove HIPPI support and RoadRunner HIPP..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11fbf852580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c06d757173270a35
dashboard link: https://syzkaller.appspot.com/bug?extid=5cf914f193dffde3bd3c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10d4a7fc580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1691f3fa580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/502d97c34968/disk-d8f87aa5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/71a9c26032b6/vmlinux-d8f87aa5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/78eeec8d5dbf/bzImage-d8f87aa5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 1 UID: 0 PID: 5987 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
RIP: 0010:ife_tlv_meta_encode+0x46/0xb0 net/ife/ife.c:166
Code: 50 83 73 f6 45 8d 77 07 4d 8d 65 04 c1 e5 10 44 89 fb 83 c3 04 09 eb 0f cb 4c 89 e8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 75 43 41 89 5d 00 41 81 e6 fc ff 00 00 41 8d 46
RSP: 0018:ffffc90003426f60 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000008000300 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000000
RBP: 0000000000030000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: ffffffff8979aa80 R12: 0000000000000004
R13: 0000000000000000 R14: 000000000000000b R15: 0000000000000004
FS:  000055557c2de500(0000) GS:ffff888125a29000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c0083cc000 CR3: 00000000763c8000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ife_encode_meta_u32+0x126/0x1c0 net/sched/act_ife.c:101
 tcf_ife_encode net/sched/act_ife.c:841 [inline]
 tcf_ife_act+0x10fd/0x1d80 net/sched/act_ife.c:877
 tc_act include/net/tc_wrapper.h:130 [inline]
 tcf_action_exec+0x185/0x8e0 net/sched/act_api.c:1152
 tc_classify include/net/tc_wrapper.h:197 [inline]
 __tcf_classify net/sched/cls_api.c:1764 [inline]
 tcf_classify+0x4cf/0x1130 net/sched/cls_api.c:1860
 multiq_classify net/sched/sch_multiq.c:39 [inline]
 multiq_enqueue+0x102/0x4d0 net/sched/sch_multiq.c:66
 dev_qdisc_enqueue+0x4e/0x240 net/core/dev.c:4146
 __dev_xmit_skb net/core/dev.c:4261 [inline]
 __dev_queue_xmit+0x1933/0x32b0 net/core/dev.c:4797
 packet_snd net/packet/af_packet.c:3076 [inline]
 packet_sendmsg+0x3eb6/0x50f0 net/packet/af_packet.c:3108
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:742
 ____sys_sendmsg+0x4d7/0x810 net/socket.c:2592
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2646
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2683 [inline]
 __se_sys_sendmsg net/socket.c:2681 [inline]
 __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2681
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2a0039acb9
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:00007fff41bd8b88 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f2a00615fa0 RCX: 00007f2a0039acb9
RDX: 0000000000000004 RSI: 00002000000000c0 RDI: 0000000000000008
RBP: 00007fff41bd8bf0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f2a00615fac R14: 00007f2a00615fa0 R15: 00007f2a00615fa0
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ife_tlv_meta_encode+0x46/0xb0 net/ife/ife.c:166
Code: 50 83 73 f6 45 8d 77 07 4d 8d 65 04 c1 e5 10 44 89 fb 83 c3 04 09 eb 0f cb 4c 89 e8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 75 43 41 89 5d 00 41 81 e6 fc ff 00 00 41 8d 46
RSP: 0018:ffffc90003426f60 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000008000300 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000000
RBP: 0000000000030000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: ffffffff8979aa80 R12: 0000000000000004
R13: 0000000000000000 R14: 000000000000000b R15: 0000000000000004
FS:  000055557c2de500(0000) GS:ffff888125a29000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c0083cc000 CR3: 00000000763c8000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	50                   	push   %rax
   1:	83 73 f6 45          	xorl   $0x45,-0xa(%rbx)
   5:	8d 77 07             	lea    0x7(%rdi),%esi
   8:	4d 8d 65 04          	lea    0x4(%r13),%r12
   c:	c1 e5 10             	shl    $0x10,%ebp
   f:	44 89 fb             	mov    %r15d,%ebx
  12:	83 c3 04             	add    $0x4,%ebx
  15:	09 eb                	or     %ebp,%ebx
  17:	0f cb                	bswap  %ebx
  19:	4c 89 e8             	mov    %r13,%rax
  1c:	48 c1 e8 03          	shr    $0x3,%rax
  20:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
  27:	fc ff df
* 2a:	0f b6 04 08          	movzbl (%rax,%rcx,1),%eax <-- trapping instruction
  2e:	84 c0                	test   %al,%al
  30:	75 43                	jne    0x75
  32:	41 89 5d 00          	mov    %ebx,0x0(%r13)
  36:	41 81 e6 fc ff 00 00 	and    $0xfffc,%r14d
  3d:	41                   	rex.B
  3e:	8d                   	.byte 0x8d
  3f:	46                   	rex.RX

---
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.