2006-10-29 17:58:45

by Oleg Nesterov

Subject: [PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

Paranoid fix. The task can free its ->mm after the 'if (p->mm)' check.

Signed-off-by: Oleg Nesterov <[email protected]>

--- STATS/kernel/tsacct.c~3_mm 2006-10-27 01:03:26.000000000 +0400
+++ STATS/kernel/tsacct.c 2006-10-29 21:46:12.000000000 +0300
@@ -80,13 +80,17 @@ void bacct_add_tsk(struct taskstats *sta
*/
void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
{
+ struct mm_struct *mm;
+
/* convert pages-jiffies to Mbyte-usec */
stats->coremem = jiffies_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
stats->virtmem = jiffies_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
- if (p->mm) {
+ mm = get_task_mm(p);
+ if (mm) {
/* adjust to KB unit */
- stats->hiwater_rss = p->mm->hiwater_rss * PAGE_SIZE / KB;
- stats->hiwater_vm = p->mm->hiwater_vm * PAGE_SIZE / KB;
+ stats->hiwater_rss = mm->hiwater_rss * PAGE_SIZE / KB;
+ stats->hiwater_vm = mm->hiwater_vm * PAGE_SIZE / KB;
+ mmput(mm);
}
stats->read_char = p->rchar;
stats->write_char = p->wchar;

2006-10-30 18:52:36

by Jay Lan

Subject: Re: [PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

Oleg Nesterov wrote:
> Paranoid fix. The task can free its ->mm after the 'if (p->mm)' check.

Why this change is necessary? This routine is indirectly invoked by
taskstats_exit_send() routine called inside do_exit():

do_exit()
{
...
taskstats_exit_send(tsk, tidstats, group_dead, mycpu);
taskstats_exit_free(tidstats);
delayacct_tsk_exit(tsk);

exit_mm(tsk);
...
}

The mm is freed in exit_mm(), right?

- jay


>
> Signed-off-by: Oleg Nesterov <[email protected]>
>
> --- STATS/kernel/tsacct.c~3_mm 2006-10-27 01:03:26.000000000 +0400
> +++ STATS/kernel/tsacct.c 2006-10-29 21:46:12.000000000 +0300
> @@ -80,13 +80,17 @@ void bacct_add_tsk(struct taskstats *sta
> */
> void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
> {
> + struct mm_struct *mm;
> +
> /* convert pages-jiffies to Mbyte-usec */
> stats->coremem = jiffies_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
> stats->virtmem = jiffies_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
> - if (p->mm) {
> + mm = get_task_mm(p);
> + if (mm) {
> /* adjust to KB unit */
> - stats->hiwater_rss = p->mm->hiwater_rss * PAGE_SIZE / KB;
> - stats->hiwater_vm = p->mm->hiwater_vm * PAGE_SIZE / KB;
> + stats->hiwater_rss = mm->hiwater_rss * PAGE_SIZE / KB;
> + stats->hiwater_vm = mm->hiwater_vm * PAGE_SIZE / KB;
> + mmput(mm);
> }
> stats->read_char = p->rchar;
> stats->write_char = p->wchar;
>

2006-10-30 20:41:36

by Oleg Nesterov

Subject: Re: [PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

On 10/30, Jay Lan wrote:
>
> Oleg Nesterov wrote:
> > Paranoid fix. The task can free its ->mm after the 'if (p->mm)' check.
>
> Why this change is necessary? This routine is indirectly invoked by
> taskstats_exit_send() routine called inside do_exit():

Not only, please note

taskstats_user_cmd(TASKSTATS_CMD_ATTR_PID)->fill_pid()->xacct_add_tsk()

path. This tsk is not 'current', it was found by find_task_by_pid(), and
it may exit at any time.

Oleg.

2006-10-31 03:08:41

by Jay Lan

Subject: Re: [PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free

Oleg Nesterov wrote:
> On 10/30, Jay Lan wrote:
>> Oleg Nesterov wrote:
>>> Paranoid fix. The task can free its ->mm after the 'if (p->mm)' check.
>> Why this change is necessary? This routine is indirectly invoked by
>> taskstats_exit_send() routine called inside do_exit():
>
> Not only, please note
>
> taskstats_user_cmd(TASKSTATS_CMD_ATTR_PID)->fill_pid()->xacct_add_tsk()
>
> path. This tsk is not 'current', it was found by find_task_by_pid(), and
> it may exit at any time.

OK. Thanks!

Acked-by: Jay Lan <[email protected]>

>
> Oleg.
>