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

[syzbot]

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=1323b770580000
kernel config: https://syzkaller.appspot.com/x/.config?x=36b0e72cad5298f8
dashboard link: https://syzkaller.appspot.com/bug?extid=d8b58d7b0ad89a678a16
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+d8b58d...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000035: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000001a8-0x00000000000001af]
CPU: 0 UID: 0 PID: 7207 Comm: syz.3.362 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:htb_deactivate net/sched/sch_htb.c:613 [inline]
RIP: 0010:htb_qlen_notify+0x31/0xc0 net/sched/sch_htb.c:1489
Code: 41 56 41 55 41 54 53 49 89 f6 49 89 ff 49 bc 00 00 00 00 00 fc ff df e8 3d c6 46 f8 49 8d 9e a8 01 00 00 49 89 dd 49 c1 ed 03 <43> 0f b6 44 25 00 84 c0 75 4d 8b 2b 31 ff 89 ee e8 5a ca 46 f8 85
RSP: 0018:ffffc90003c6efb0 EFLAGS: 00010206
RAX: ffffffff89798833 RBX: 00000000000001a8 RCX: ffff8880585d9e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff888058d42000
RBP: dffffc0000000000 R08: ffff8880585d9e00 R09: 0000000000000002
R10: 00000000ffffffff R11: ffffffff89798810 R12: dffffc0000000000
R13: 0000000000000035 R14: 0000000000000000 R15: ffff888058d42000
FS: 00007f22a32406c0(0000) GS:ffff888125c50000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f22a31ddd58 CR3: 000000007c196000 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_change+0x1519/0x1f50 net/sched/sch_fq.c:1147
fq_init+0x699/0x960 net/sched/sch_fq.c:1201
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: 0033:0x7f22a238e929
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:00007f22a3240038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f22a25b5fa0 RCX: 00007f22a238e929
RDX: 0000000000000800 RSI: 0000200000000100 RDI: 0000000000000008
RBP: 00007f22a2410b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f22a25b5fa0 R15: 00007fffce377518
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:htb_deactivate net/sched/sch_htb.c:613 [inline]
RIP: 0010:htb_qlen_notify+0x31/0xc0 net/sched/sch_htb.c:1489
Code: 41 56 41 55 41 54 53 49 89 f6 49 89 ff 49 bc 00 00 00 00 00 fc ff df e8 3d c6 46 f8 49 8d 9e a8 01 00 00 49 89 dd 49 c1 ed 03 <43> 0f b6 44 25 00 84 c0 75 4d 8b 2b 31 ff 89 ee e8 5a ca 46 f8 85
RSP: 0018:ffffc90003c6efb0 EFLAGS: 00010206
RAX: ffffffff89798833 RBX: 00000000000001a8 RCX: ffff8880585d9e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff888058d42000
RBP: dffffc0000000000 R08: ffff8880585d9e00 R09: 0000000000000002
R10: 00000000ffffffff R11: ffffffff89798810 R12: dffffc0000000000
R13: 0000000000000035 R14: 0000000000000000 R15: ffff888058d42000
FS: 00007f22a32406c0(0000) GS:ffff888125c50000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f22a31ddd58 CR3: 000000007c196000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 41 56 push %r14
2: 41 55 push %r13
4: 41 54 push %r12
6: 53 push %rbx
7: 49 89 f6 mov %rsi,%r14
a: 49 89 ff mov %rdi,%r15
d: 49 bc 00 00 00 00 00 movabs $0xdffffc0000000000,%r12
14: fc ff df
17: e8 3d c6 46 f8 call 0xf846c659
1c: 49 8d 9e a8 01 00 00 lea 0x1a8(%r14),%rbx
23: 49 89 dd mov %rbx,%r13
26: 49 c1 ed 03 shr $0x3,%r13
* 2a: 43 0f b6 44 25 00 movzbl 0x0(%r13,%r12,1),%eax <-- trapping instruction
30: 84 c0 test %al,%al
32: 75 4d jne 0x81
34: 8b 2b mov (%rbx),%ebp
36: 31 ff xor %edi,%edi
38: 89 ee mov %ebp,%esi
3a: e8 5a ca 46 f8 call 0xf846ca99
3f: 85 .byte 0x85


---
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#syz undup

[syzbot]

syzbot has found a reproducer for 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=15cc0582580000

kernel config: https://syzkaller.appspot.com/x/.config?x=36b0e72cad5298f8
dashboard link: https://syzkaller.appspot.com/bug?extid=d8b58d7b0ad89a678a16
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1113748c580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10909ebc580000

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+d8b58d...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000035: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000001a8-0x00000000000001af]

CPU: 1 UID: 0 PID: 6017 Comm: syz.0.16 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:htb_deactivate net/sched/sch_htb.c:613 [inline]
RIP: 0010:htb_qlen_notify+0x31/0xc0 net/sched/sch_htb.c:1489
Code: 41 56 41 55 41 54 53 49 89 f6 49 89 ff 49 bc 00 00 00 00 00 fc ff df e8 3d c6 46 f8 49 8d 9e a8 01 00 00 49 89 dd 49 c1 ed 03 <43> 0f b6 44 25 00 84 c0 75 4d 8b 2b 31 ff 89 ee e8 5a ca 46 f8 85

RSP: 0018:ffffc900034f6fb0 EFLAGS: 00010206
RAX: ffffffff89798833 RBX: 00000000000001a8 RCX: ffff88802714bc00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807a6ac000
RBP: dffffc0000000000 R08: ffff88802714bc00 R09: 0000000000000002

R10: 00000000ffffffff R11: ffffffff89798810 R12: dffffc0000000000

R13: 0000000000000035 R14: 0000000000000000 R15: ffff88807a6ac000
FS: 00007fa0c3df16c0(0000) GS:ffff888125d50000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fa0c3dd0d58 CR3: 00000000743e8000 CR4: 00000000003526f0

RIP: 0033:0x7fa0c2f8e929

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:00007fa0c3df1038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fa0c31b5fa0 RCX: 00007fa0c2f8e929
RDX: 0000000000044080 RSI: 0000200000000040 RDI: 0000000000000006
RBP: 00007fa0c3010b39 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 00007fa0c31b5fa0 R15: 00007ffd14aa8178

</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:htb_deactivate net/sched/sch_htb.c:613 [inline]
RIP: 0010:htb_qlen_notify+0x31/0xc0 net/sched/sch_htb.c:1489
Code: 41 56 41 55 41 54 53 49 89 f6 49 89 ff 49 bc 00 00 00 00 00 fc ff df e8 3d c6 46 f8 49 8d 9e a8 01 00 00 49 89 dd 49 c1 ed 03 <43> 0f b6 44 25 00 84 c0 75 4d 8b 2b 31 ff 89 ee e8 5a ca 46 f8 85

RSP: 0018:ffffc900034f6fb0 EFLAGS: 00010206
RAX: ffffffff89798833 RBX: 00000000000001a8 RCX: ffff88802714bc00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807a6ac000
RBP: dffffc0000000000 R08: ffff88802714bc00 R09: 0000000000000002

R10: 00000000ffffffff R11: ffffffff89798810 R12: dffffc0000000000

R13: 0000000000000035 R14: 0000000000000000 R15: ffff88807a6ac000
FS: 00007fa0c3df16c0(0000) GS:ffff888125d50000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fa0c3dd0d58 CR3: 00000000743e8000 CR4: 00000000003526f0

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.

[Jamal Hadi Salim]

On Thu, Jul 3, 2025 at 11:05 AM Jamal Hadi Salim <j...@mojatatu.com> wrote:

>
> On Thu, Jul 3, 2025 at 7:32 AM syzbot
> <syzbot+d8b58d...@syzkaller.appspotmail.com> wrote:
> >
> > syzbot has found a reproducer for the following issue on:
> >
> > HEAD commit: bd475eeaaf3c Merge branch '200GbE' of git://git.kernel.org..
> > git tree: net

[..]
> It is triggered by your patch. On the first try, removing your patch
> seems to fix it.
> It may have nothing to do with your patch i.e your patch may have
> opened it up to trigger an existing bug.
> You removed that if n=0, len=0 check which earlier code was using to
> terminate the processing.
>

Ok, after some more digging - this is not a bug you caused but rather
one you exposed.
We are looking into it.

cheers,
jamal
> cheers,
> jamal

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+d8b58d...@syzkaller.appspotmail.com
Tested-by: syzbot+d8b58d...@syzkaller.appspotmail.com

Tested on:

commit: 223e2288 vsock/vmci: Clear the vmci transport packet p..
git tree: net
console output: https://syzkaller.appspot.com/x/log.txt?x=16685ebc580000

kernel config: https://syzkaller.appspot.com/x/.config?x=36b0e72cad5298f8
dashboard link: https://syzkaller.appspot.com/bug?extid=d8b58d7b0ad89a678a16
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

patch: https://syzkaller.appspot.com/x/patch.diff?x=141d8c8c580000

Note: testing is done by a robot and is best-effort only.

[Victor Nogueira]

On 7/3/25 08:32, syzbot wrote:
> syzbot has found a reproducer for 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=15cc0582580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=36b0e72cad5298f8
> dashboard link: https://syzkaller.appspot.com/bug?extid=d8b58d7b0ad89a678a16
> compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1113748c580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10909ebc580000

#syz test

[Jamal Hadi Salim]

On Thu, Jul 3, 2025 at 7:32 AM syzbot
<syzbot+d8b58d...@syzkaller.appspotmail.com> wrote:
>

It is triggered by your patch. On the first try, removing your patch
seems to fix it.
It may have nothing to do with your patch i.e your patch may have
opened it up to trigger an existing bug.
You removed that if n=0, len=0 check which earlier code was using to
terminate the processing.

cheers,
jamal

[syzbot]

syzbot has bisected this issue to:

commit 103406b38c600fec1fe375a77b27d87e314aea09
Author: Lion Ackermann <nna...@gmail.com>
Date: Mon Jun 30 13:27:30 2025 +0000

net/sched: Always pass notifications when child class becomes empty

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14c9c582580000
start commit: bd475eeaaf3c Merge branch '200GbE' of git://git.kernel.org..
git tree: net
final oops: https://syzkaller.appspot.com/x/report.txt?x=16c9c582580000
console output: https://syzkaller.appspot.com/x/log.txt?x=12c9c582580000

kernel config: https://syzkaller.appspot.com/x/.config?x=36b0e72cad5298f8
dashboard link: https://syzkaller.appspot.com/bug?extid=d8b58d7b0ad89a678a16

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=171af48c580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=151b33d4580000

Reported-by: syzbot+d8b58d...@syzkaller.appspotmail.com
Fixes: 103406b38c60 ("net/sched: Always pass notifications when child class becomes empty")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection