Commit ad133ba3 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

sched, signals: fix the racy usage of ->signal in account_group_xxx/run_posix_cpu_timers 



Impact: fix potential NULL dereference

Contrary to ad474cac changelog, other
acct_group_xxx() helpers can be called after exit_notify() by timer tick.
Thanks to Roland for pointing out this. Somehow I missed this simple fact
when I read the original patch, and I am afraid I confused Frank during
the discussion. Sorry.

Fortunately, these helpers work with current, we can check ->exit_state
to ensure that ->signal can't go away under us.

Also, add the comment and compiler barrier to account_group_exec_runtime(),
to make sure we load ->signal only once.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 29d7b90c

kernel/posix-cpu-timers.c

+5 −2
Original line number Diff line number Diff line
@@ -1308,9 +1308,10 @@ static inline int task_cputime_expired(const struct task_cputime *sample, 
 */

static inline int fastpath_timer_check(struct task_struct *tsk)

{

	struct signal_struct *sig = tsk->signal;

	struct signal_struct *sig;



	if (unlikely(!sig))

	/* tsk == current, ensure it is safe to use ->signal/sighand */

	if (unlikely(tsk->exit_state))

		return 0;



	if (!task_cputime_zero(&tsk->cputime_expires)) {
@@ -1323,6 +1324,8 @@ static inline int fastpath_timer_check(struct task_struct *tsk) 
		if (task_cputime_expired(&task_sample, &tsk->cputime_expires))

			return 1;

	}



	sig = tsk->signal;

	if (!task_cputime_zero(&sig->cputime_expires)) {

		struct task_cputime group_sample;

kernel/sched_stats.h

+11 −4
Original line number Diff line number Diff line
@@ -298,9 +298,11 @@ static inline void account_group_user_time(struct task_struct *tsk, 
{

	struct signal_struct *sig;



	sig = tsk->signal;

	if (unlikely(!sig))

	/* tsk == current, ensure it is safe to use ->signal */

	if (unlikely(tsk->exit_state))

		return;



	sig = tsk->signal;

	if (sig->cputime.totals) {

		struct task_cputime *times;
@@ -325,9 +327,11 @@ static inline void account_group_system_time(struct task_struct *tsk, 
{

	struct signal_struct *sig;



	sig = tsk->signal;

	if (unlikely(!sig))

	/* tsk == current, ensure it is safe to use ->signal */

	if (unlikely(tsk->exit_state))

		return;



	sig = tsk->signal;

	if (sig->cputime.totals) {

		struct task_cputime *times;
@@ -353,8 +357,11 @@ static inline void account_group_exec_runtime(struct task_struct *tsk, 
	struct signal_struct *sig;



	sig = tsk->signal;

	/* see __exit_signal()->task_rq_unlock_wait() */

	barrier();

	if (unlikely(!sig))

		return;



	if (sig->cputime.totals) {

		struct task_cputime *times;

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