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Commit 329f7dba authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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[PATCH] fix de_thread() vs send_group_sigqueue() race 



When non-leader thread does exec, de_thread calls release_task(leader) before
calling exit_itimers(). If local timer interrupt happens in between, it can
oops in send_group_sigqueue() while taking ->sighand->siglock == NULL.

However, we can't change send_group_sigqueue() to check p->signal != NULL,
because sys_timer_create() does get_task_struct() only in SIGEV_THREAD_ID
case. So it is possible that this task_struct was already freed and we can't
trust p->signal.

This patch changes de_thread() so that leader released after exit_itimers()
call.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarChris Wright <chrisw@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent a52e8381

fs/exec.c

+7 −3
Original line number Diff line number Diff line
@@ -590,6 +590,7 @@ static inline int de_thread(struct task_struct *tsk) 
	struct signal_struct *sig = tsk->signal;

	struct sighand_struct *newsighand, *oldsighand = tsk->sighand;

	spinlock_t *lock = &oldsighand->siglock;

	struct task_struct *leader = NULL;

	int count;



	/*
@@ -665,7 +666,7 @@ static inline int de_thread(struct task_struct *tsk) 
	 * and to assume its PID:

	 */

	if (!thread_group_leader(current)) {

		struct task_struct *leader = current->group_leader, *parent;

		struct task_struct *parent;

		struct dentry *proc_dentry1, *proc_dentry2;

		unsigned long exit_state, ptrace;
@@ -674,6 +675,7 @@ static inline int de_thread(struct task_struct *tsk) 
		 * It should already be zombie at this point, most

		 * of the time.

		 */

		leader = current->group_leader;

		while (leader->exit_state != EXIT_ZOMBIE)

			yield();
@@ -733,7 +735,6 @@ static inline int de_thread(struct task_struct *tsk) 
		proc_pid_flush(proc_dentry2);



		BUG_ON(exit_state != EXIT_ZOMBIE);

		release_task(leader);

        }



	/*
@@ -743,8 +744,11 @@ static inline int de_thread(struct task_struct *tsk) 
	sig->flags = 0;



no_thread_group:

	BUG_ON(atomic_read(&sig->count) != 1);

	exit_itimers(sig);

	if (leader)

		release_task(leader);



	BUG_ON(atomic_read(&sig->count) != 1);



	if (atomic_read(&oldsighand->count) == 1) {

		/*