linux-kernel - BUG: unable to handle kernel paging request from pty

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Message-ID: <56CED373.9060603@suse.cz>
Date:	Thu, 25 Feb 2016 11:12:03 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, stable@...r.kernel.org
Cc:	lwn@....net, Jiri Slaby <jslaby@...e.cz>,
	Peter Hurley <peter@...leysoftware.com>
Subject: BUG: unable to handle kernel paging request from pty_write [was:
 Linux 4.4.2]

On 02/17/2016, 09:37 PM, Greg KH wrote:
> I'm announcing the release of the 4.4.2 kernel.
...
> Peter Hurley (4):
>       n_tty: Fix unsafe reference to "other" ldisc
>       tty: Wait interruptibly for tty lock on reopen
>       tty: Retry failed reopen if tty teardown in-progress
>       tty: Fix unsafe ldisc reference via ioctl(TIOCGETD)

It seems like 4.4.2 schedules a tty flush work but the work is deleted
meanwhile. This was trigerred by a gdb build on our servers [1]. Going
to investigate further, if this doesn't ring a bell?

[1]
https://build.opensuse.org/package/live_build_log/openSUSE:Factory:Staging:I/gdb/standard/x86_64

kernel tried to execute NX-protected page - exploit attempt? (uid: 399)
BUG: unable to handle kernel paging request at ffff88023fd40000
IP: [<ffff88023fd40000>] 0xffff88023fd40000
PGD 2240067 PUD 23fced063 PMD 23fcee063 PTE 800000023fd40163
Oops: 0011 [#1] PREEMPT SMP
Modules linked in: ata_generic ata_piix nls_iso8859_1 nls_cp437 vfat fat
virtio_rng virtio_blk virtio_pci virtio
k_ipv6 nf_defrag_ipv6 nf_conntrack btrfs xor raid6_pq reiserfs squashfs
fuse dm_snapshot dm_bufio dm_mod binfmt_
misc loop sg
CPU: 7 PID: 3127 Comm: gdb Not tainted 4.4.2-3-default #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2
014
task: ffff8801e43a4240 ti: ffff8800bb2a4000 task.ti: ffff8800bb2a4000
RIP: 0010:[<ffff88023fd40000>]  [<ffff88023fd40000>] 0xffff88023fd40000
RSP: 0018:ffff8800bb2a7c50  EFLAGS: 00056686
RAX: 00000000bb37e180 RBX: 0000000000000001 RCX: 00000000ffffffff
RDX: 0000000000000000 RSI: ffff88023fdd6e80 RDI: ffff88023fdd6e80
RBP: ffffffff810a535a R08: 0000000000000000 R09: 0000000000000020
R10: 0000000001b52cb0 R11: 0000000000000293 R12: 0000000000000046
R13: ffff8800bb37e180 R14: 0000000000016e80 R15: ffff8800bb2a7c80
FS:  00007fe3e4aba740(0000) GS:ffff88023fdc0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88023fd40000 CR3: 00000002353cd000 CR4: 00000000000406e0
Stack:
 000000008146e197 ffff88017ee19f00 ffff880234e26a08 ffff88017ed2a830
 0000000000000005 0000000000010e30 ffff8800bb2a7c90 ffffffff810a5585
 ffff8800bb2a7cc8 ffffffff81092fe1 0000000000000000 ffff88017ee19f00
Call Trace:
Inexact backtrace:

 [<ffffffff810a5585>] ? wake_up_process+0x15/0x20
 [<ffffffff81092fe1>] ? insert_work+0x81/0xc0
 [<ffffffff8109326c>] ? __queue_work+0x24c/0x390
 [<ffffffff81093947>] ? queue_work_on+0x27/0x40
 [<ffffffff814732db>] ? tty_flip_buffer_push+0x2b/0x30
 [<ffffffff81474f1a>] ? pty_write+0x4a/0x60
 [<ffffffff8146e5c6>] ? n_tty_write+0x1b6/0x4d0
 [<ffffffff810bd330>] ? __wake_up_sync+0x20/0x20
 [<ffffffff8146a96b>] ? tty_write+0x1cb/0x2b0
 [<ffffffff8146e410>] ? n_tty_open+0xe0/0xe0
 [<ffffffff811fa858>] ? __vfs_write+0x28/0xf0
 [<ffffffff81334a48>] ? apparmor_file_permission+0x18/0x20
 [<ffffffff812ff05d>] ? security_file_permission+0x3d/0xc0
 [<ffffffff811facbf>] ? rw_verify_area+0x4f/0xe0
 [<ffffffff811faf29>] ? vfs_write+0xa9/0x1a0
 [<ffffffff811fbb26>] ? SyS_write+0x46/0xa0
 [<ffffffff816a96f6>] ? entry_SYSCALL_64_fastpath+0x16/0x75
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 0
00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
RIP  [<ffff88023fd40000>] 0xffff88023fd40000
 RSP <ffff8800bb2a7c50>
CR2: ffff88023fd40000
---[ end trace 14d86b882766d1bf ]---

thanks,
-- 
js
suse labs