[syzbot ci] Re: net/sched: Introduce qdisc quirk_chk op

[syzbot ci <syzbot+ci4f0c6bd07d511716@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v1] net/sched: Introduce qdisc quirk_chk op
https://lore.kernel.org/all/20251124223749.503979-1-victor@mojatatu.com
* [RFC PATCH net-next] net/sched: Introduce qdisc quirk_chk op

and found the following issue:
general protection fault in netem_quirk_chk

Full report is available here:
https://ci.syzbot.org/series/0ba1b5b2-32e5-45b5-9ede-1290a7852d5e

***

general protection fault in netem_quirk_chk

tree:      net-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
base:      e2c20036a8879476c88002730d8a27f4e3c32d4b
arch:      amd64
compiler:  Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config:    https://ci.syzbot.org/builds/0064d8bc-3c48-4267-9b5e-0f43a8514002/config
C repro:   https://ci.syzbot.org/findings/17d4a158-13d5-439e-8a4d-10e6e40a2ab1/c_repro
syz repro: https://ci.syzbot.org/findings/17d4a158-13d5-439e-8a4d-10e6e40a2ab1/syz_repro

netlink: 28 bytes leftover after parsing attributes in process `syz.0.17'.
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
CPU: 1 UID: 0 PID: 5959 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:netem_quirk_chk+0x37/0x660 net/sched/sch_netem.c:999
Code: 53 48 83 ec 30 48 89 54 24 08 49 89 f7 48 89 fd 49 be 00 00 00 00 00 fc ff df e8 e4 68 67 f8 49 83 c7 14 4c 89 f8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 a0 05 00 00 41 8b 37 31 ff 89 74 24 04
RSP: 0018:ffffc90003737260 EFLAGS: 00010203
RAX: 0000000000000002 RBX: dffffc0000000000 RCX: ffff888113168000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8881139f3000
RBP: ffff8881139f3000 R08: ffff888113168000 R09: 0000000000000002
R10: 00000000fffffff1 R11: ffffffff89589ab0 R12: ffff8881166a0000
R13: ffffffff89589ab0 R14: dffffc0000000000 R15: 0000000000000014
FS:  0000555559c83500(0000) GS:ffff8882a9f35000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000100 CR3: 000000010a1b0000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 qdisc_create+0x73f/0xf10 net/sched/sch_api.c:1319
 __tc_modify_qdisc net/sched/sch_api.c:1765 [inline]
 tc_modify_qdisc+0x1582/0x2140 net/sched/sch_api.c:1829
 rtnetlink_rcv_msg+0x77c/0xb70 net/core/rtnetlink.c:6967
 netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
 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: 0033:0x7fe6bff8f749
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:00007fff10f91288 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fe6c01e5fa0 RCX: 00007fe6bff8f749
RDX: 0000000000000000 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007fe6c0013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe6c01e5fa0 R14: 00007fe6c01e5fa0 R15: 0000000000000003
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:netem_quirk_chk+0x37/0x660 net/sched/sch_netem.c:999
Code: 53 48 83 ec 30 48 89 54 24 08 49 89 f7 48 89 fd 49 be 00 00 00 00 00 fc ff df e8 e4 68 67 f8 49 83 c7 14 4c 89 f8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 0f 85 a0 05 00 00 41 8b 37 31 ff 89 74 24 04
RSP: 0018:ffffc90003737260 EFLAGS: 00010203
RAX: 0000000000000002 RBX: dffffc0000000000 RCX: ffff888113168000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8881139f3000
RBP: ffff8881139f3000 R08: ffff888113168000 R09: 0000000000000002
R10: 00000000fffffff1 R11: ffffffff89589ab0 R12: ffff8881166a0000
R13: ffffffff89589ab0 R14: dffffc0000000000 R15: 0000000000000014
FS:  0000555559c83500(0000) GS:ffff8882a9f35000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000100 CR3: 000000010a1b0000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
   0:	53                   	push   %rbx
   1:	48 83 ec 30          	sub    $0x30,%rsp
   5:	48 89 54 24 08       	mov    %rdx,0x8(%rsp)
   a:	49 89 f7             	mov    %rsi,%r15
   d:	48 89 fd             	mov    %rdi,%rbp
  10:	49 be 00 00 00 00 00 	movabs $0xdffffc0000000000,%r14
  17:	fc ff df
  1a:	e8 e4 68 67 f8       	call   0xf8676903
  1f:	49 83 c7 14          	add    $0x14,%r15
  23:	4c 89 f8             	mov    %r15,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 0f b6 04 30       	movzbl (%rax,%r14,1),%eax <-- trapping instruction
  2f:	84 c0                	test   %al,%al
  31:	0f 85 a0 05 00 00    	jne    0x5d7
  37:	41 8b 37             	mov    (%r15),%esi
  3a:	31 ff                	xor    %edi,%edi
  3c:	89 74 24 04          	mov    %esi,0x4(%rsp)


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

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