linux-kernel - Re: tty: tty_struct memory leak

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Date:	Thu, 4 Feb 2016 11:48:02 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: tty: tty_struct memory leak

On Thu, Feb 4, 2016 at 12:27 AM, Peter Hurley <peter@...leysoftware.com> wrote:
> Hi Dmitry,
>
> On 02/03/2016 08:26 AM, Dmitry Vyukov wrote:
>> On Wed, Feb 3, 2016 at 5:10 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>>> Hello,
>>>
>>> The following program causes tty_struct memory leak:
>>>
>>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>>> #include <pthread.h>
>>> #include <stdint.h>
>>> #include <string.h>
>>> #include <sys/syscall.h>
>>> #include <unistd.h>
>>>
>>> int main()
>>> {
>>>   alarm(1);
>>>   syscall(SYS_open, "/dev/ircomm7", 0x12d401ul, 0, 0, 0);
>>>   return 0;
>>> }
>
> Going to need more information than this because the reproducer
> above does not generate a tty_struct memory leak.
>
> Here's what I did:
>
> Enabled tty debugging and added patch below [1] to show kfree(tty), then:
>
> $ sudo modprobe ircomm
> $ ./reproducer
>
> Here's what I got:
>
> [ 1436.864342] tty_ldisc_open: ircomm ircomm7: ffff8802aa3b3410: opened
> [ 1436.864352] tty_open: ircomm ircomm7: opening (count=1)
> [ 1437.863994] tty_open: ircomm ircomm7: open error -512, releasing
> [ 1437.864051] tty_release: ircomm ircomm7: releasing (count=1)
> [ 1437.864055] tty_wait_until_sent: ircomm ircomm7: wait until sent, timeout=7500
> [ 1437.864110] tty_release: ircomm ircomm7: final close
> [ 1437.864120] tty_ldisc_close: ircomm ircomm7: ffff8802aa3b3410: closed
> [ 1437.864124] tty_ldisc_release: ircomm ircomm7: released
> [ 1437.864130] tty_release: ircomm ircomm7: release
> [ 1437.864148] release_one_tty: ircomm ircomm7: freeing structure
>                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Note that release_one_tty() ends in kfree(tty)


There seems to be some race, please try this one:

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <pthread.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

void work()
{
  alarm(1);
  syscall(SYS_open, "/dev/ircomm7", 0x12d401ul, 0, 0, 0);
}

int main() {
  int running, status;

  for (;;) {
    while (running < 32) {
      if (fork() == 0) {
        work();
        exit(0);
      }
      running++;
    }
    if (wait(&status) > 0)
      running--;
  }
}


If I sample /proc/slabinfo while it runs:

# cat /proc/slabinfo | egrep "^kmalloc-2048"

Number of allocated objects constantly grow.