Messages in this thread Patch in this message | | | Date | Mon, 30 Oct 2006 10:51:58 -0800 | From | Jay Lan <> | Subject | Re: [PATCH] xacct_add_tsk: fix pure theoretical ->mm use-after-free |
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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 <oleg@tv-sign.ru> > > --- 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; >
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