[v6.6] general protection fault in dummy_queue

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: da47cbc25466 Linux 6.6.144
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=179886b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=776f67b58dca4e701ca7
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6988639f2873/disk-da47cbc2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/796fa32e7777/vmlinux-da47cbc2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/480ca9c40b5c/bzImage-da47cbc2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+776f67...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc000000000a: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057]
CPU: 0 PID: 5435 Comm: dhcpcd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:dummy_queue+0x1a7/0x8c0 drivers/usb/gadget/udc/dummy_hcd.c:717
Code: fc ff df 80 3c 08 00 74 08 4c 89 e7 e8 82 cd 25 fb 4d 8b 24 24 49 83 c4 50 4c 89 e0 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 ea 05 00 00 45 8b 24 24 44 89 e6 83 e6 02
RSP: 0018:ffffc900037d7020 EFLAGS: 00010206
RAX: 000000000000000a RBX: ffff8881472c6f10 RCX: dffffc0000000000
RDX: ffff888027191e00 RSI: 0000000000000003 RDI: 0000000000000005
RBP: ffff8881472c6f00 R08: ffffffff911e85c7 R09: 1ffffffff223d0b8
R10: dffffc0000000000 R11: fffffbfff223d0b9 R12: 0000000000000050
R13: 1ffff11028e58de0 R14: ffff8881417b40e0 R15: ffff8881417b4c00
FS: 00007fbfd6d90740(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd252307e0 CR3: 000000002fe7d000 CR4: 00000000003506f0
Call Trace:
<TASK>
usb_ep_queue+0xea/0x350 drivers/usb/gadget/udc/core.c:303
eth_start_xmit+0xa51/0x1130 drivers/usb/gadget/function/u_ether.c:578
__netdev_start_xmit include/linux/netdevice.h:4943 [inline]
netdev_start_xmit include/linux/netdevice.h:4957 [inline]
xmit_one net/core/dev.c:3644 [inline]
dev_hard_start_xmit+0x269/0x790 net/core/dev.c:3660
sch_direct_xmit+0x251/0x4a0 net/sched/sch_generic.c:345
__dev_xmit_skb net/core/dev.c:3881 [inline]
__dev_queue_xmit+0x162a/0x3630 net/core/dev.c:4416
dev_queue_xmit include/linux/netdevice.h:3113 [inline]
neigh_hh_output include/net/neighbour.h:527 [inline]
neigh_output include/net/neighbour.h:541 [inline]
ip6_finish_output2+0xdf7/0x1620 net/ipv6/ip6_output.c:141
ip6_send_skb+0x1cd/0x380 net/ipv6/ip6_output.c:1979
rawv6_push_pending_frames+0x74d/0x930 net/ipv6/raw.c:581
rawv6_sendmsg+0x12db/0x1740 net/ipv6/raw.c:920
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
____sys_sendmsg+0x61b/0x980 net/socket.c:2595
___sys_sendmsg+0x2a6/0x360 net/socket.c:2649
__sys_sendmsg net/socket.c:2678 [inline]
__do_sys_sendmsg net/socket.c:2687 [inline]
__se_sys_sendmsg+0x1d0/0x2c0 net/socket.c:2685
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fbfd6e1a407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffd25220630 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fbfd6d90740 RCX: 00007fbfd6e1a407
RDX: 0000000000000000 RSI: 00007ffd252307e0 RDI: 000000000000000d
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007ffd25240a10
R13: 0000000000000002 R14: 0000000000000010 R15: 00007ffd252307e0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:dummy_queue+0x1a7/0x8c0 drivers/usb/gadget/udc/dummy_hcd.c:717
Code: fc ff df 80 3c 08 00 74 08 4c 89 e7 e8 82 cd 25 fb 4d 8b 24 24 49 83 c4 50 4c 89 e0 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 ea 05 00 00 45 8b 24 24 44 89 e6 83 e6 02
RSP: 0018:ffffc900037d7020 EFLAGS: 00010206
RAX: 000000000000000a RBX: ffff8881472c6f10 RCX: dffffc0000000000
RDX: ffff888027191e00 RSI: 0000000000000003 RDI: 0000000000000005
RBP: ffff8881472c6f00 R08: ffffffff911e85c7 R09: 1ffffffff223d0b8
R10: dffffc0000000000 R11: fffffbfff223d0b9 R12: 0000000000000050
R13: 1ffff11028e58de0 R14: ffff8881417b40e0 R15: ffff8881417b4c00
FS: 00007fbfd6d90740(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd252307e0 CR3: 000000002fe7d000 CR4: 00000000003506f0
----------------
Code disassembly (best guess):
0: fc cld
1: ff lcall (bad)
2: df 80 3c 08 00 74 filds 0x7400083c(%rax)
8: 08 4c 89 e7 or %cl,-0x19(%rcx,%rcx,4)
c: e8 82 cd 25 fb call 0xfb25cd93
11: 4d 8b 24 24 mov (%r12),%r12
15: 49 83 c4 50 add $0x50,%r12
19: 4c 89 e0 mov %r12,%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: 0f 85 ea 05 00 00 jne 0x620
36: 45 8b 24 24 mov (%r12),%r12d
3a: 44 89 e6 mov %r12d,%esi
3d: 83 e6 02 and $0x2,%esi


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