Date:   Sun, 12 Feb 2023 09:00:17 -0800
From:   Dipanjan Das <mail.dipanjan.das@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>, jirislaby@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     syzkaller <syzkaller@...glegroups.com>,
        Marius Fleischer <fleischermarius@...glemail.com>,
        Priyanka Bose <its.priyanka.bose@...il.com>
Subject: BUG: unable to handle kernel paging request in n_tty_open

Hi,

We would like to report the following bug which has been found by our
modified version of syzkaller.

======================================================
description: BUG: unable to handle kernel paging request in n_tty_open
affected file: drivers/tty/tty_ldisc.c
kernel version: 6.2.0-rc5
kernel commit: 41c66f47061608dc1fd493eebce198f0e74cc2d7
git tree: kmsan
kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=a9a22da1efde3af6
crash reproducer: attached
======================================================
Crash log:
======================================================
RBP: 00007f7117670c30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000d
R13: 00007f71165abf6c R14: 00007f71165abf60 R15: 00007f7117670d80
 </TASK>
BUG: unable to handle page fault for address: ffffd10016bfa050
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 11410067 P4D 11410067 PUD 1157d067 PMD 31910067 PTE 0
Oops: 0002 [#1] PREEMPT SMP
CPU: 1 PID: 14496 Comm: syz-executor.4 Not tainted
6.2.0-rc5-00010-g41c66f470616 #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:n_tty_open+0xa5/0x240 drivers/tty/n_tty.c:1883
Code: c8 48 c7 c7 c0 79 c0 8f e8 f8 0e ef fb 4d 8d 67 50 48 8b 18 8b
02 89 45 d0 4d 85 ed 0f 85 12 01 00 00 4c 89 e7 e8 0b 0f ef fb <48> 89
18 48 85 db 0f 85 0b 01 00 00 4d 8d a7 88 22 00 00 48 8b 45
RSP: 0018:ffff8880a72036a0 EFLAGS: 00010286
RAX: ffffd10016bfa050 RBX: 0000000000000000 RCX: ffffd10016bfa050
RDX: ffffd90016bfa050 RSI: 0000000000000001 RDI: ffffc90016bfa050
RBP: ffff8880a72036e0 R08: 0000000000000001 R09: ffff8880a6a03458
R10: 0000000000000001 R11: 0000000000000000 R12: ffffc90016bfa050
R13: 0000000000000000 R14: ffff88808b6c1000 R15: ffffc90016bfa000
FS:  00007f7117671700(0000) GS:ffff88813fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffd10016bfa050 CR3: 00000000a7110000 CR4: 0000000000150ee0
Call Trace:
 <TASK>
 tty_ldisc_open drivers/tty/tty_ldisc.c:433 [inline]
 tty_ldisc_setup+0xfc/0x4c0 drivers/tty/tty_ldisc.c:740
 tty_init_dev+0x4b0/0xad0 drivers/tty/tty_io.c:1437
 tty_open_by_driver drivers/tty/tty_io.c:2079 [inline]
 tty_open+0x176f/0x20b0 drivers/tty/tty_io.c:2126
 chrdev_open+0xa45/0xb80 fs/char_dev.c:414
 do_dentry_open+0xf85/0x1970 fs/open.c:882
 vfs_open+0x75/0xa0 fs/open.c:1013
 do_open fs/namei.c:3557 [inline]
 path_openat+0x4c4b/0x5a00 fs/namei.c:3714
 do_filp_open+0x252/0x660 fs/namei.c:3741
 do_sys_openat2+0x200/0x920 fs/open.c:1310
 do_sys_open fs/open.c:1326 [inline]
 __do_sys_openat fs/open.c:1342 [inline]
 __se_sys_openat fs/open.c:1337 [inline]
 __x64_sys_openat+0x285/0x310 fs/open.c:1337
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f711648d59d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7117670bd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f71165abf60 RCX: 00007f711648d59d
RDX: 00000000000a6503 RSI: 0000000020000000 RDI: ffffffffffffff9c
RBP: 00007f7117670c30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000d
R13: 00007f71165abf6c R14: 00007f71165abf60 R15: 00007f7117670d80
 </TASK>
Modules linked in:
CR2: ffffd10016bfa050
---[ end trace 0000000000000000 ]---
RIP: 0010:n_tty_open+0xa5/0x240 drivers/tty/n_tty.c:1883
Code: c8 48 c7 c7 c0 79 c0 8f e8 f8 0e ef fb 4d 8d 67 50 48 8b 18 8b
02 89 45 d0 4d 85 ed 0f 85 12 01 00 00 4c 89 e7 e8 0b 0f ef fb <48> 89
18 48 85 db 0f 85 0b 01 00 00 4d 8d a7 88 22 00 00 48 8b 45
RSP: 0018:ffff8880a72036a0 EFLAGS: 00010286
RAX: ffffd10016bfa050 RBX: 0000000000000000 RCX: ffffd10016bfa050
RDX: ffffd90016bfa050 RSI: 0000000000000001 RDI: ffffc90016bfa050
RBP: ffff8880a72036e0 R08: 0000000000000001 R09: ffff8880a6a03458
R10: 0000000000000001 R11: 0000000000000000 R12: ffffc90016bfa050
R13: 0000000000000000 R14: ffff88808b6c1000 R15: ffffc90016bfa000
FS:  00007f7117671700(0000) GS:ffff88813fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffd10016bfa050 CR3: 00000000a7110000 CR4: 0000000000150ee0
----------------
Code disassembly (best guess):
   0: c8 48 c7 c7          enterq $0xc748,$0xc7
   4: c0 79 c0 8f          sarb   $0x8f,-0x40(%rcx)
   8: e8 f8 0e ef fb        callq  0xfbef0f05
   d: 4d 8d 67 50          lea    0x50(%r15),%r12
  11: 48 8b 18              mov    (%rax),%rbx
  14: 8b 02                mov    (%rdx),%eax
  16: 89 45 d0              mov    %eax,-0x30(%rbp)
  19: 4d 85 ed              test   %r13,%r13
  1c: 0f 85 12 01 00 00    jne    0x134
  22: 4c 89 e7              mov    %r12,%rdi
  25: e8 0b 0f ef fb        callq  0xfbef0f35
* 2a: 48 89 18              mov    %rbx,(%rax) <-- trapping instruction
  2d: 48 85 db              test   %rbx,%rbx
  30: 0f 85 0b 01 00 00    jne    0x141
  36: 4d 8d a7 88 22 00 00 lea    0x2288(%r15),%r12
  3d: 48                    rex.W
  3e: 8b                    .byte 0x8b
  3f: 45                    rex.RB

-- 
Thanks and Regards,

Dipanjan

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