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[PATCH] bacct_add_tsk: fix unsafe and wrong parent/group_leader dereference

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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 <[email protected]>
Cc: Shailabh Nagar <[email protected]>
Cc: Balbir Singh <[email protected]>
Acked-by: Jay Lan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Oleg Nesterov 2006-10-28 10:38:50 -07:00 • committed by Linus Torvalds
commit 05d5bcd60e
1 changed files with 5 additions and 2 deletions
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7
kernel/tsacct.c
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@ -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;