[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 <oleg@tv-sign.ru> Cc: Shailabh Nagar <nagar@watson.ibm.com> Cc: Balbir Singh <balbir@in.ibm.com> Acked-by: Jay Lan <jlan@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -36,7 +36,7 @@ void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk)
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/* calculate task elapsed time in timespec */
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do_posix_clock_monotonic_gettime(&uptime);
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ts = timespec_sub(uptime, current->group_leader->start_time);
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ts = timespec_sub(uptime, tsk->start_time);
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/* rebase elapsed time to usec */
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ac_etime = timespec_to_ns(&ts);
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do_div(ac_etime, NSEC_PER_USEC);
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@ -58,7 +58,10 @@ void bacct_add_tsk(struct taskstats *stats, struct task_struct *tsk)
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stats->ac_uid = tsk->uid;
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stats->ac_gid = tsk->gid;
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stats->ac_pid = tsk->pid;
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stats->ac_ppid = (tsk->parent) ? tsk->parent->pid : 0;
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rcu_read_lock();
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stats->ac_ppid = pid_alive(tsk) ?
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rcu_dereference(tsk->real_parent)->tgid : 0;
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rcu_read_unlock();
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stats->ac_utime = cputime_to_msecs(tsk->utime) * USEC_PER_MSEC;
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stats->ac_stime = cputime_to_msecs(tsk->stime) * USEC_PER_MSEC;
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stats->ac_minflt = tsk->min_flt;
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