Re: BUG: unable to handle kernel paging request in devpts_mntget

[Eric Biggers]

On Fri, Nov 03, 2017 at 05:42:01AM -0700, syzbot wrote:
> Hello,
> 
> syzkaller hit the following crash on
> 36ef71cae353f88fd6e095e2aaa3e5953af1685d
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> 
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
> 
> 
> IP: devpts_mntget+0x135/0x280 fs/devpts/inode.c:173
> PGD 7fff4067 P4D 7fff4067 PUD 7fff3067 PMD 7fff2067 PTE 0
> Oops: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 0 PID: 4725 Comm: syz-executor2 Not tainted 4.14.0-rc5-next-20171018+
> #8
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff88006ba222c0 task.stack: ffff880068f00000
> RIP: 0010:devpts_mntget+0x135/0x280 fs/devpts/inode.c:173
> RSP: 0018:ffff880068f07a50 EFLAGS: 00010a03
> RAX: dffffc0000000000 RBX: ffffffffffffffed RCX: ffffffff81ce4ac0
> RDX: 1ffffffffffffffe RSI: 0000000000000001 RDI: fffffffffffffff5
> RBP: ffff880068f07ae0 R08: 0000000000000001 R09: 1ffff1000d1e0f05
> R10: ffff880068f07760 R11: 0000000000000000 R12: 1ffff1000d1e0f4a
> R13: ffff880068f07a70 R14: ffff88006bc44700 R15: ffff880068f07b20
> FS:  00007f907b47d700(0000) GS:ffff88003ec00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: fffffbfffffffffe CR3: 000000003e167000 CR4: 00000000000006f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  ptm_open_peer+0x11a/0x2f0 drivers/tty/pty.c:631
>  tty_ioctl+0x50f/0x15f0 drivers/tty/tty_io.c:2621
>  vfs_ioctl fs/ioctl.c:45 [inline]
>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
>  SYSC_ioctl fs/ioctl.c:700 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>  entry_SYSCALL_64_fastpath+0x1f/0xbe
> RIP: 0033:0x447c89
> RSP: 002b:00007f907b47cbd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f907b47d6cc RCX: 0000000000447c89
> RDX: 00000000202c2000 RSI: 2000000000005441 RDI: 0000000000000000
> RBP: 0000000000000082 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 0000000000008e08 R14: 00000000006ecea8 R15: 00007f907b47d700
> Code: c1 ea 03 80 3c 02 00 0f 85 56 01 00 00 48 8b 5d 90 e8 e0 73 a0 ff 48
> 8d 7b 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f
> 85 24 01 00 00 4c 8b 7b 08 48 b8 00 00 00 00 00
> RIP: devpts_mntget+0x135/0x280 fs/devpts/inode.c:173 RSP: ffff880068f07a50
> CR2: fffffbfffffffffe
> ---[ end trace 47949eeac6e2cd68 ]---
> Kernel panic - not syncing: Fatal exception
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@xxxxxxxxxxxxxxxxx
> Please credit me with: Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
> 
> syzbot will keep track of this bug report.
> Once a fix for this bug is committed, please reply to this email with:
> #syz fix: exact-commit-title

Fixed by commit c9cc8d01fb0411:

#syz fix: devpts: fix error handling in devpts_mntget()

- Eric