[syzbot] [net?] general protection fault in hfsc_qlen_notify

[syzbot <syzbot+5eccb463fa89309d8bdc@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    bd475eeaaf3c Merge branch '200GbE' of git://git.kernel.org..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=16510c8c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=36b0e72cad5298f8
dashboard link: https://syzkaller.appspot.com/bug?extid=5eccb463fa89309d8bdc
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d59bc82a55e0/disk-bd475eea.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2a83759fceb6/vmlinux-bd475eea.xz
kernel image: https://storage.googleapis.com/syzbot-assets/07576fd8e432/bzImage-bd475eea.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5eccb463fa89309d8bdc@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc000000005d: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000002e8-0x00000000000002ef]
CPU: 0 UID: 0 PID: 13767 Comm: syz.0.2184 Not tainted 6.16.0-rc3-syzkaller-00144-gbd475eeaaf3c #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:hfsc_qlen_notify+0x2e/0x160 net/sched/sch_hfsc.c:1238
Code: 55 41 57 41 56 41 55 41 54 53 48 89 f3 49 bc 00 00 00 00 00 fc ff df e8 d0 ef 45 f8 4c 8d b3 ec 02 00 00 4c 89 f0 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 e8 00 00 00 41 8b 2e 31 ff 89 ee e8 e9
RSP: 0018:ffffc90003d2f070 EFLAGS: 00010203
RAX: 000000000000005d RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc9000c0e9000 RSI: 0000000000000323 RDI: 0000000000000324
RBP: dffffc0000000000 R08: ffff88802c831e00 R09: 0000000000000002
R10: 00000000ffffffff R11: ffffffff897a5e80 R12: dffffc0000000000
R13: ffff888053eaa000 R14: 00000000000002ec R15: ffff888053eaa000
FS:  00007f783fff36c0(0000) GS:ffff888125c50000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8d435e1e9c CR3: 000000005e97a000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 qdisc_tree_reduce_backlog+0x29c/0x480 net/sched/sch_api.c:811
 fq_codel_change+0xa96/0xef0 net/sched/sch_fq_codel.c:450
 fq_codel_init+0x355/0x960 net/sched/sch_fq_codel.c:487
 qdisc_create+0x7ac/0xea0 net/sched/sch_api.c:1324
 __tc_modify_qdisc net/sched/sch_api.c:1749 [inline]
 tc_modify_qdisc+0x1426/0x2010 net/sched/sch_api.c:1813
 rtnetlink_rcv_msg+0x779/0xb70 net/core/rtnetlink.c:6953
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x75b/0x8d0 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x21c/0x270 net/socket.c:727
 ____sys_sendmsg+0x505/0x830 net/socket.c:2566
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
 __sys_sendmsg net/socket.c:2652 [inline]
 __do_sys_sendmsg net/socket.c:2657 [inline]
 __se_sys_sendmsg net/socket.c:2655 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f783f18e929
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:00007f783fff3038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f783f3b5fa0 RCX: 00007f783f18e929
RDX: 0000000000000800 RSI: 0000200000000100 RDI: 0000000000000005
RBP: 00007f783f210b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f783f3b5fa0 R15: 00007ffd53451d68
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:hfsc_qlen_notify+0x2e/0x160 net/sched/sch_hfsc.c:1238
Code: 55 41 57 41 56 41 55 41 54 53 48 89 f3 49 bc 00 00 00 00 00 fc ff df e8 d0 ef 45 f8 4c 8d b3 ec 02 00 00 4c 89 f0 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 e8 00 00 00 41 8b 2e 31 ff 89 ee e8 e9
RSP: 0018:ffffc90003d2f070 EFLAGS: 00010203
RAX: 000000000000005d RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc9000c0e9000 RSI: 0000000000000323 RDI: 0000000000000324
RBP: dffffc0000000000 R08: ffff88802c831e00 R09: 0000000000000002
R10: 00000000ffffffff R11: ffffffff897a5e80 R12: dffffc0000000000
R13: ffff888053eaa000 R14: 00000000000002ec R15: ffff888053eaa000
FS:  00007f783fff36c0(0000) GS:ffff888125c50000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8d435e1e9c CR3: 000000005e97a000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	55                   	push   %rbp
   1:	41 57                	push   %r15
   3:	41 56                	push   %r14
   5:	41 55                	push   %r13
   7:	41 54                	push   %r12
   9:	53                   	push   %rbx
   a:	48 89 f3             	mov    %rsi,%rbx
   d:	49 bc 00 00 00 00 00 	movabs $0xdffffc0000000000,%r12
  14:	fc ff df
  17:	e8 d0 ef 45 f8       	call   0xf845efec
  1c:	4c 8d b3 ec 02 00 00 	lea    0x2ec(%rbx),%r14
  23:	4c 89 f0             	mov    %r14,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 0f b6 04 20       	movzbl (%rax,%r12,1),%eax <-- trapping instruction
  2f:	84 c0                	test   %al,%al
  31:	0f 85 e8 00 00 00    	jne    0x11f
  37:	41 8b 2e             	mov    (%r14),%ebp
  3a:	31 ff                	xor    %edi,%edi
  3c:	89 ee                	mov    %ebp,%esi
  3e:	e8                   	.byte 0xe8
  3f:	e9                   	.byte 0xe9


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