From: Oleg Nesterov Date: Sat, 28 Oct 2006 17:38:50 +0000 (-0700) Subject: [PATCH] bacct_add_tsk: fix unsafe and wrong parent/group_leader dereference X-Git-Tag: v2.6.19-rc4~43 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=05d5bcd60e8202e5c7b28cf61186043a4d612623;p=linux-2.6-omap-h63xx.git [PATCH] bacct_add_tsk: fix unsafe and wrong parent/group_leader dereference 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. 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 ? Signed-off-by: Oleg Nesterov Cc: Shailabh Nagar Cc: Balbir Singh Acked-by: Jay Lan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/tsacct.c b/kernel/tsacct.c index db443221ba5..65a5036a3d9 100644 --- a/kernel/tsacct.c +++ b/kernel/tsacct.c @@ -36,7 +36,7 @@ void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk) /* 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 *stats, struct task_struct *tsk) 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;