syzbot


BUG: unable to handle kernel paging request in vcs_read

Status: moderation: reported on 2025/08/26 12:11
Subsystems: serial
[Documentation on labels]
Reported-by: syzbot+ccdf05c3420fdbd12e55@syzkaller.appspotmail.com
First crash: 6d00h, last: 6d00h
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-out-of-bounds Read in vcs_read serial 17 1 205d 201d 0/29 auto-obsoleted due to no activity on 2025/05/05 08:36
upstream KMSAN: kernel-infoleak in vcs_read (2) serial 18 C 1556 938d 2093d 22/29 fixed on 2023/02/24 13:50

Sample crash report:
BUG: unable to handle page fault for address: ffff887f9e4df0a0
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0 
Oops: Oops: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 8526 Comm: syz.3.541 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:vcs_scr_readw+0x75/0xd0 drivers/tty/vt/vt.c:4999
Code: 51 2b 5d fc 48 89 da 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 0f b6 14 02 48 89 d8 83 e0 07 83 c0 01 38 d0 7c 04 84 d2 75 40 <0f> b7 2b e8 23 2b 5d fc 5b 89 e8 5d c3 cc cc cc cc e8 15 2b 5d fc
RSP: 0018:ffffc9000c137bd8 EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff887f9e4df0a0 RCX: ffffffff855ddd35
RDX: 0000000000000000 RSI: ffffffff855ddd3f RDI: 0000000000000006
RBP: ffff8880258974ce R08: 0000000000000006 R09: ffff8880258974ce
R10: ffff887f9e4df0a0 R11: ffffffff82202dea R12: 0000000000000000
R13: ffff888035083006 R14: ffff887f9e4df0a0 R15: ffff887f9e4df0a2
FS:  00007fd1c43676c0(0000) GS:ffff8881246c3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff887f9e4df0a0 CR3: 000000001cee8000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 vcs_read_buf drivers/tty/vt/vc_screen.c:352 [inline]
 vcs_read+0x636/0xbe0 drivers/tty/vt/vc_screen.c:444
 vfs_read+0x1e1/0xcf0 fs/read_write.c:570
 ksys_pread64 fs/read_write.c:763 [inline]
 __do_sys_pread64 fs/read_write.c:771 [inline]
 __se_sys_pread64 fs/read_write.c:768 [inline]
 __x64_sys_pread64+0x1eb/0x250 fs/read_write.c:768
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd1c358ebe9
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:00007fd1c4367038 EFLAGS: 00000246 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007fd1c37b5fa0 RCX: 00007fd1c358ebe9
RDX: 000000000000c721 RSI: 0000200000000040 RDI: 0000000000000006
RBP: 00007fd1c3611e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd1c37b6038 R14: 00007fd1c37b5fa0 R15: 00007ffc597f2638
 </TASK>
Modules linked in:
CR2: ffff887f9e4df0a0
---[ end trace 0000000000000000 ]---
RIP: 0010:vcs_scr_readw+0x75/0xd0 drivers/tty/vt/vt.c:4999
Code: 51 2b 5d fc 48 89 da 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 0f b6 14 02 48 89 d8 83 e0 07 83 c0 01 38 d0 7c 04 84 d2 75 40 <0f> b7 2b e8 23 2b 5d fc 5b 89 e8 5d c3 cc cc cc cc e8 15 2b 5d fc
RSP: 0018:ffffc9000c137bd8 EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff887f9e4df0a0 RCX: ffffffff855ddd35
RDX: 0000000000000000 RSI: ffffffff855ddd3f RDI: 0000000000000006
RBP: ffff8880258974ce R08: 0000000000000006 R09: ffff8880258974ce
R10: ffff887f9e4df0a0 R11: ffffffff82202dea R12: 0000000000000000
R13: ffff888035083006 R14: ffff887f9e4df0a0 R15: ffff887f9e4df0a2
FS:  00007fd1c43676c0(0000) GS:ffff8881246c3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff887f9e4df0a0 CR3: 000000001cee8000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	51                   	push   %rcx
   1:	2b 5d fc             	sub    -0x4(%rbp),%ebx
   4:	48 89 da             	mov    %rbx,%rdx
   7:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
   e:	fc ff df
  11:	48 c1 ea 03          	shr    $0x3,%rdx
  15:	0f b6 14 02          	movzbl (%rdx,%rax,1),%edx
  19:	48 89 d8             	mov    %rbx,%rax
  1c:	83 e0 07             	and    $0x7,%eax
  1f:	83 c0 01             	add    $0x1,%eax
  22:	38 d0                	cmp    %dl,%al
  24:	7c 04                	jl     0x2a
  26:	84 d2                	test   %dl,%dl
  28:	75 40                	jne    0x6a
* 2a:	0f b7 2b             	movzwl (%rbx),%ebp <-- trapping instruction
  2d:	e8 23 2b 5d fc       	call   0xfc5d2b55
  32:	5b                   	pop    %rbx
  33:	89 e8                	mov    %ebp,%eax
  35:	5d                   	pop    %rbp
  36:	c3                   	ret
  37:	cc                   	int3
  38:	cc                   	int3
  39:	cc                   	int3
  3a:	cc                   	int3
  3b:	e8 15 2b 5d fc       	call   0xfc5d2b55

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/22 12:06 upstream 3957a5720157 bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci-qemu-gce-upstream-auto BUG: unable to handle kernel paging request in vcs_read
* Struck through repros no longer work on HEAD.