Subject: [syzbot] [atm?] general protection fault in atmtcp_ioctl

From: syzbot <[email-masked]>
Date: Wed, 22 Apr 2026 00:51:42 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    1f5ffc672165 Fix mismerge of the arm64 / timer-core interr..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14b72c36580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=95729ed00549063a
dashboard link: https://syzkaller.appspot.com/bug?extid=52bbaea57234493b6b17
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6b552538b97f/disk-1f5ffc67.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/724a3a1d69d7/vmlinux-1f5ffc67.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ea684969e2c2/bzImage-1f5ffc67.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: 15453 Comm: syz.2.2407 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:atmtcp_attach drivers/atm/atmtcp.c:408 [inline]
RIP: 0010:atmtcp_ioctl+0x860/0xdf0 drivers/atm/atmtcp.c:477
Code: ff e9 b4 fb ff ff 4c 8d 63 20 4c 89 e0 48 c1 e8 03 80 3c 28 00 74 08 4c 89 e7 e8 cb 21 0b fb 4d 8b 24 24 4c 89 e0 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 e7 e8 b2 21 0b fb 49 83 3c 24 00 0f 84 f0
RSP: 0018:ffffc9000f6b7c30 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff888037f2f000 RCX: ffffffff8bb4829e
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffffc9000f6b7b80
RBP: dffffc0000000000 R08: ffffc9000f6b7b87 R09: 1ffff92001ed6f70
R10: dffffc0000000000 R11: fffff52001ed6f71 R12: 0000000000000000
R13: 1ffff11006fe5e00 R14: ffff88808ac0d440 R15: ffff88803234e000
FS:  00007fd42b7c26c0(0000) GS:ffff888125345000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001944 CR3: 00000000358e6000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 do_vcc_ioctl+0x36d/0x9d0 net/atm/ioctl.c:159
 sock_do_ioctl+0x101/0x320 net/socket.c:1313
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1434
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd42a99c819
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:00007fd42b7c2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd42ac15fa0 RCX: 00007fd42a99c819
RDX: 0000000000000000 RSI: 0000000000006180 RDI: 0000000000000008
RBP: 00007fd42aa32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd42ac16038 R14: 00007fd42ac15fa0 R15: 00007ffe8b9d1618
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:atmtcp_attach drivers/atm/atmtcp.c:408 [inline]
RIP: 0010:atmtcp_ioctl+0x860/0xdf0 drivers/atm/atmtcp.c:477
Code: ff e9 b4 fb ff ff 4c 8d 63 20 4c 89 e0 48 c1 e8 03 80 3c 28 00 74 08 4c 89 e7 e8 cb 21 0b fb 4d 8b 24 24 4c 89 e0 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 e7 e8 b2 21 0b fb 49 83 3c 24 00 0f 84 f0
RSP: 0018:ffffc9000f6b7c30 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff888037f2f000 RCX: ffffffff8bb4829e
RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffffc9000f6b7b80
RBP: dffffc0000000000 R08: ffffc9000f6b7b87 R09: 1ffff92001ed6f70
R10: dffffc0000000000 R11: fffff52001ed6f71 R12: 0000000000000000
R13: 1ffff11006fe5e00 R14: ffff88808ac0d440 R15: ffff88803234e000
FS:  00007fd42b7c26c0(0000) GS:ffff888125345000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c3d9593 CR3: 00000000358e6000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	ff                   	ljmp   (bad)
   1:	e9 b4 fb ff ff       	jmp    0xfffffbba
   6:	4c 8d 63 20          	lea    0x20(%rbx),%r12
   a:	4c 89 e0             	mov    %r12,%rax
   d:	48 c1 e8 03          	shr    $0x3,%rax
  11:	80 3c 28 00          	cmpb   $0x0,(%rax,%rbp,1)
  15:	74 08                	je     0x1f
  17:	4c 89 e7             	mov    %r12,%rdi
  1a:	e8 cb 21 0b fb       	call   0xfb0b21ea
  1f:	4d 8b 24 24          	mov    (%r12),%r12
  23:	4c 89 e0             	mov    %r12,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	80 3c 28 00          	cmpb   $0x0,(%rax,%rbp,1) <-- trapping instruction
  2e:	74 08                	je     0x38
  30:	4c 89 e7             	mov    %r12,%rdi
  33:	e8 b2 21 0b fb       	call   0xfb0b21ea
  38:	49 83 3c 24 00       	cmpq   $0x0,(%r12)
  3d:	0f                   	.byte 0xf
  3e:	84 f0                	test   %dh,%al

---
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