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-ker...@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. <ballo...@debian.org>
Imagine a large red swirl here.
/* Copyright © 2016 Bill Allombert
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
Check the License for details. You should have received a copy of it, along
with the package; see the file 'COPYING'. If not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/tiocl.h>
#include <stdint.h>
#include <linux/kd.h>
#include <time.h>
static void
select(void)
{
int fd;
struct {
char argp[2]; /*Force struct alignment*/
struct tiocl_selection sel;
} s;
s.argp[0] = 0; /* unused */
s.argp[1] = TIOCL_SETSEL;
s.sel.xs = 1;
s.sel.ys = 1;
s.sel.xe = 10;
s.sel.ye = 10;
s.sel.sel_mode = TIOCL_SELCHAR;
fd = open("/dev/tty0",O_RDONLY);
if (ioctl(fd, TIOCLINUX, ((char*)&s)+1) < 0)
perror("selection: TIOCLINUX");
close(fd);
}
void paste(void)
{
int fd;
char subcode = TIOCL_PASTESEL;
fd = open("/dev/tty0", O_RDWR);
if (ioctl(fd, TIOCLINUX, &subcode)<0)
perror("paste: TIOCLINUX");
close(fd);
}
int main(void)
{
int n=0, i;
struct timespec req, rem;
req.tv_sec = 0;
req.tv_nsec = 200000000;
for(i=0; i<25*130; i++) fputc('@',stderr);
select();
while(1)
{
fprintf(stderr,"try %d\n",n++);
paste();
nanosleep(&req, &rem);
}
}
