[syzbot] [serial?] general protection fault in vc_deallocate

[syzbot <syzbot+f6cb41c144427dc0796a@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    3e8e5822146b Add linux-next specific files for 20250908
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11984642580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=69cfefa929ab96f7
dashboard link: https://syzkaller.appspot.com/bug?extid=f6cb41c144427dc0796a
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17230934580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15984642580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eaa87d8bc6ca/disk-3e8e5822.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6640e70f5002/vmlinux-3e8e5822.xz
kernel image: https://storage.googleapis.com/syzbot-assets/40f622291050/bzImage-3e8e5822.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f6cb41c144427dc0796a@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc00000000b2: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000590-0x0000000000000597]
CPU: 0 UID: 0 PID: 6062 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:vc_deallocate+0x303/0x3e0 drivers/tty/vt/vt.c:1345
Code: e8 f2 1f d7 fc 49 c7 07 00 00 00 00 eb 0e e8 14 1d 73 fc eb 05 e8 0d 1d 73 fc 31 db 4c 8d b3 90 05 00 00 4d 89 f4 49 c1 ec 03 <43> 80 3c 2c 00 74 08 4c 89 f7 e8 ce 1e d7 fc 4d 8b 3e 4d 85 ff 74
RSP: 0018:ffffc900035f79e0 EFLAGS: 00010206
RAX: ffffffff854c8f03 RBX: 0000000000000000 RCX: ffff88807dd3dac0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 000000000000003f
RBP: ffffc900035f7a90 R08: ffffffff8fc3c7cf R09: 1ffffffff1f878f9
R10: dffffc0000000000 R11: fffffbfff1f878fa R12: 00000000000000b2
R13: dffffc0000000000 R14: 0000000000000590 R15: ffffffff9a034a30
FS:  000055557fa10500(0000) GS:ffff8881259f1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557fa10808 CR3: 000000007ba62000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 vt_disallocate_all+0x60/0xe0 drivers/tty/vt/vt_ioctl.c:652
 vt_ioctl+0x1adc/0x1f20 drivers/tty/vt/vt_ioctl.c:886
 tty_ioctl+0x926/0xde0 drivers/tty/tty_io.c:2792
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
 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: 0033:0x7f97fa38ebe9
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:00007ffe553801c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f97fa5c5fa0 RCX: 00007f97fa38ebe9
RDX: 0000000000000000 RSI: 0000000000005608 RDI: 0000000000000004
RBP: 00007f97fa411e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f97fa5c5fa0 R14: 00007f97fa5c5fa0 R15: 0000000000000002
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:vc_deallocate+0x303/0x3e0 drivers/tty/vt/vt.c:1345
Code: e8 f2 1f d7 fc 49 c7 07 00 00 00 00 eb 0e e8 14 1d 73 fc eb 05 e8 0d 1d 73 fc 31 db 4c 8d b3 90 05 00 00 4d 89 f4 49 c1 ec 03 <43> 80 3c 2c 00 74 08 4c 89 f7 e8 ce 1e d7 fc 4d 8b 3e 4d 85 ff 74
RSP: 0018:ffffc900035f79e0 EFLAGS: 00010206
RAX: ffffffff854c8f03 RBX: 0000000000000000 RCX: ffff88807dd3dac0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 000000000000003f
RBP: ffffc900035f7a90 R08: ffffffff8fc3c7cf R09: 1ffffffff1f878f9
R10: dffffc0000000000 R11: fffffbfff1f878fa R12: 00000000000000b2
R13: dffffc0000000000 R14: 0000000000000590 R15: ffffffff9a034a30
FS:  000055557fa10500(0000) GS:ffff8881259f1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557fa10808 CR3: 000000007ba62000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	e8 f2 1f d7 fc       	call   0xfcd71ff7
   5:	49 c7 07 00 00 00 00 	movq   $0x0,(%r15)
   c:	eb 0e                	jmp    0x1c
   e:	e8 14 1d 73 fc       	call   0xfc731d27
  13:	eb 05                	jmp    0x1a
  15:	e8 0d 1d 73 fc       	call   0xfc731d27
  1a:	31 db                	xor    %ebx,%ebx
  1c:	4c 8d b3 90 05 00 00 	lea    0x590(%rbx),%r14
  23:	4d 89 f4             	mov    %r14,%r12
  26:	49 c1 ec 03          	shr    $0x3,%r12
* 2a:	43 80 3c 2c 00       	cmpb   $0x0,(%r12,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 f7             	mov    %r14,%rdi
  34:	e8 ce 1e d7 fc       	call   0xfcd71f07
  39:	4d 8b 3e             	mov    (%r14),%r15
  3c:	4d 85 ff             	test   %r15,%r15
  3f:	74                   	.byte 0x74


---
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