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Bug#849474: repeated console pasting with TIOCLINUX+TIOCL_PASTESEL hung process

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Package: src:linux
Version: 3.16.36-1+deb8u2
Severity: normal

Dear Linux team,

I found that quickly repeatedly pasting lot of text in the console using
the TIOCLINUX system call and the TIOCL_PASTESEL option cause the
calling process to hung in kernel mode, making it unkillable while
using 100% CPU, and hanging the shutdown of the system and other
negative effect.

This syscall requires the user to be root, however software like gpm and
consolation allow a non priviledged user to do it, by selecting a big
chunk of text and pasting it several time a second (with the mouse).

This can be automated using the attached program
(warning, this is slightly dangerous since it copy-paste dummy text to
the console, be careful. It is safer to use it in a X terminal since then
the pasted text is sent to the underlying VT which is disabled, but it
is less reliable)

gcc -O3 -Wall crash.c -o crash
sudo ./crash

I found that the larger the number of pasted characters and the faster it is done,
the quicker the process hangs.

-- Package-specific info:
** Version:
Linux version 3.16.0-4-amd64 (debian-kernel@lists.debian.org) (gcc version 4.8.4 (Debian 4.8.4-1) ) #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19)

** Command line:
BOOT_IMAGE=/boot/vmlinuz-3.16.0-4-amd64 root=UUID=f91ea73c-a9e5-440f-98eb-f99554b362e1 ro quiet

** Not tainted

Log:

Dec 27 14:02:16 yellowpig kernel: [  240.410094] INFO: task kworker/1:2:226 blocked for more than 120 seconds.
Dec 27 14:02:16 yellowpig kernel: [  240.414447]       Not tainted 3.16.0-4-amd64 #1
Dec 27 14:02:16 yellowpig kernel: [  240.419214] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 27 14:02:16 yellowpig kernel: [  240.423708] kworker/1:2     D ffff8802434eefb8     0   226      2 0x00000000
Dec 27 14:02:16 yellowpig kernel: [  240.423744] Workqueue: events flush_to_ldisc
Dec 27 14:02:16 yellowpig kernel: [  240.423756]  ffff8802434eeb60 0000000000000046 0000000000012f40 ffff880243b17fd8
Dec 27 14:02:16 yellowpig kernel: [  240.423764]  0000000000012f40 ffff8802434eeb60 ffff88024e81e428 ffff880243b17dd0
Dec 27 14:02:16 yellowpig kernel: [  240.423772]  ffff88024e81e42c ffff8802434eeb60 00000000ffffffff ffff88024e81e430
Dec 27 14:02:16 yellowpig kernel: [  240.423780] Call Trace:
Dec 27 14:02:16 yellowpig kernel: [  240.423797]  [<ffffffff815151d5>] ? schedule_preempt_disabled+0x25/0x70
Dec 27 14:02:16 yellowpig kernel: [  240.423824]  [<ffffffff81516c33>] ? __mutex_lock_slowpath+0xd3/0x1c0
Dec 27 14:02:16 yellowpig kernel: [  240.423836]  [<ffffffff81074076>] ? lock_timer_base.isra.35+0x26/0x50
Dec 27 14:02:16 yellowpig kernel: [  240.423844]  [<ffffffff81516d3b>] ? mutex_lock+0x1b/0x2a
Dec 27 14:02:16 yellowpig kernel: [  240.423865]  [<ffffffff8137202a>] ? flush_to_ldisc+0x4a/0x140
Dec 27 14:02:16 yellowpig kernel: [  240.423875]  [<ffffffff81082b73>] ? process_one_work+0x143/0x430
Dec 27 14:02:16 yellowpig kernel: [  240.423889]  [<ffffffff810832f3>] ? worker_thread+0x113/0x4f0
Dec 27 14:02:16 yellowpig kernel: [  240.423898]  [<ffffffff81514951>] ? __schedule+0x2b1/0x6f0
Dec 27 14:02:16 yellowpig kernel: [  240.423912]  [<ffffffff810831e0>] ? rescuer_thread+0x2d0/0x2d0
Dec 27 14:02:16 yellowpig kernel: [  240.423921]  [<ffffffff810894bd>] ? kthread+0xbd/0xe0
Dec 27 14:02:16 yellowpig kernel: [  240.423940]  [<ffffffff81089400>] ? kthread_create_on_node+0x180/0x180
Dec 27 14:02:16 yellowpig kernel: [  240.423953]  [<ffffffff815184d8>] ? ret_from_fork+0x58/0x90
Dec 27 14:02:16 yellowpig kernel: [  240.423962]  [<ffffffff81089400>] ? kthread_create_on_node+0x180/0x180

Cheers,
-- 
Bill. <ballombe@debian.org>

Imagine a large red swirl here. 

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Bug#849474: repeated console pasting with TIOCLINUX+TIOCL_PASTESEL hung process Bill Allombert <ballombe@debian.org> - 2016-12-27 16:10 +0100

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