Messages in this thread | | | Date | Fri, 27 Oct 2006 10:40:53 -0700 | From | Jay Lan <> | Subject | Re: [PATCH 2/6] bacct_add_tsk: fix unsafe and wrong parent/group_leader dereference |
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Oleg Nesterov wrote: > 1. ts = timespec_sub(uptime, current->group_leader->start_time); > > It is possible that current != tsk. Probably it was supposed > to be 'tsk->group_leader->start_time. But why we are reading > group_leader's start_time ? This accounting is per thread, > not per procees, I changed this to 'tsk->start_time. > Please corect me.
This is right. Thanks!
> > 2. stats->ac_ppid = (tsk->parent) ? tsk->parent->pid : 0; > > tsk->parent never == NULL, and it is unsafe to dereference it. > Both the task and it's parent may exit after the caller unlocks > tasklist_lock, the memory could be unmapped (DEBUG_SLAB). > (And we should use ->real_parent->tgid in fact). > > Q: I don't understand the 'if (thread_group_leader(tsk))' check. > Why it is needed ?
The code was borrowed from kernel/acct.c. The CSA code was extended from the BSD accounting, so we just borrowed the basic accounting stuff from the code.
Thanks, - jay
> > Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> > > --- STATS/kernel/tsacct.c~2_par_fix 2006-10-22 18:24:03.000000000 +0400 > +++ STATS/kernel/tsacct.c 2006-10-27 01:03:26.000000000 +0400 > @@ -36,7 +36,7 @@ void bacct_add_tsk(struct taskstats *sta > > /* calculate task elapsed time in timespec */ > do_posix_clock_monotonic_gettime(&uptime); > - ts = timespec_sub(uptime, current->group_leader->start_time); > + ts = timespec_sub(uptime, tsk->start_time); > /* rebase elapsed time to usec */ > ac_etime = timespec_to_ns(&ts); > do_div(ac_etime, NSEC_PER_USEC); > @@ -58,7 +58,10 @@ void bacct_add_tsk(struct taskstats *sta > stats->ac_uid = tsk->uid; > stats->ac_gid = tsk->gid; > stats->ac_pid = tsk->pid; > - stats->ac_ppid = (tsk->parent) ? tsk->parent->pid : 0; > + rcu_read_lock(); > + stats->ac_ppid = pid_alive(tsk) ? > + rcu_dereference(tsk->real_parent)->tgid : 0; > + rcu_read_unlock(); > stats->ac_utime = cputime_to_msecs(tsk->utime) * USEC_PER_MSEC; > stats->ac_stime = cputime_to_msecs(tsk->stime) * USEC_PER_MSEC; > stats->ac_minflt = tsk->min_flt; >
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