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Commit 9f96cb1e authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Linus Torvalds
Browse files

robust futex thread exit race 



Calling handle_futex_death in exit_robust_list for the different robust
mutexes of a thread basically frees the mutex.  Another thread might grab
the lock immediately which updates the next pointer of the mutex.
fetch_robust_entry over the next pointer might therefore branch into the
robust mutex list of a different thread.  This can cause two problems: 1)
some mutexes held by the dead thread are not getting freed and 2) some
mutexs held by a different thread are freed.

The next point need to be read before calling handle_futex_death.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8792f961

kernel/futex.c

+16 −10
Original line number Diff line number Diff line
@@ -1943,9 +1943,10 @@ static inline int fetch_robust_entry(struct robust_list __user **entry, 
void exit_robust_list(struct task_struct *curr)

{

	struct robust_list_head __user *head = curr->robust_list;

	struct robust_list __user *entry, *pending;

	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;

	struct robust_list __user *entry, *next_entry, *pending;

	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;

	unsigned long futex_offset;

	int rc;



	/*

	 * Fetch the list head (which was registered earlier, via
@@ -1965,11 +1966,13 @@ void exit_robust_list(struct task_struct *curr) 
	if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))

		return;



	if (pending)

		handle_futex_death((void __user *)pending + futex_offset,

				   curr, pip);



	next_entry = NULL;	/* avoid warning with gcc */

	while (entry != &head->list) {

		/*

		 * Fetch the next entry in the list before calling

		 * handle_futex_death:

		 */

		rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);

		/*

		 * A pending lock might already be on the list, so

		 * don't process it twice:
@@ -1978,11 +1981,10 @@ void exit_robust_list(struct task_struct *curr) 
			if (handle_futex_death((void __user *)entry + futex_offset,

						curr, pi))

				return;

		/*

		 * Fetch the next entry in the list:

		 */

		if (fetch_robust_entry(&entry, &entry->next, &pi))

		if (rc)

			return;

		entry = next_entry;

		pi = next_pi;

		/*

		 * Avoid excessively long or circular lists:

		 */
@@ -1991,6 +1993,10 @@ void exit_robust_list(struct task_struct *curr) 


		cond_resched();

	}



	if (pending)

		handle_futex_death((void __user *)pending + futex_offset,

				   curr, pip);

}



long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,

kernel/futex_compat.c

+18 −10
Original line number Diff line number Diff line
@@ -38,10 +38,11 @@ fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry, 
void compat_exit_robust_list(struct task_struct *curr)

{

	struct compat_robust_list_head __user *head = curr->compat_robust_list;

	struct robust_list __user *entry, *pending;

	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;

	compat_uptr_t uentry, upending;

	struct robust_list __user *entry, *next_entry, *pending;

	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;

	compat_uptr_t uentry, next_uentry, upending;

	compat_long_t futex_offset;

	int rc;



	/*

	 * Fetch the list head (which was registered earlier, via
@@ -61,10 +62,15 @@ void compat_exit_robust_list(struct task_struct *curr) 
	if (fetch_robust_entry(&upending, &pending,

			       &head->list_op_pending, &pip))

		return;

	if (pending)

		handle_futex_death((void __user *)pending + futex_offset, curr, pip);



	next_entry = NULL;	/* avoid warning with gcc */

	while (entry != (struct robust_list __user *) &head->list) {

		/*

		 * Fetch the next entry in the list before calling

		 * handle_futex_death:

		 */

		rc = fetch_robust_entry(&next_uentry, &next_entry,

			(compat_uptr_t __user *)&entry->next, &next_pi);

		/*

		 * A pending lock might already be on the list, so

		 * dont process it twice:
@@ -74,12 +80,11 @@ void compat_exit_robust_list(struct task_struct *curr) 
						curr, pi))

				return;



		/*

		 * Fetch the next entry in the list:

		 */

		if (fetch_robust_entry(&uentry, &entry,

				       (compat_uptr_t __user *)&entry->next, &pi))

		if (rc)

			return;

		uentry = next_uentry;

		entry = next_entry;

		pi = next_pi;

		/*

		 * Avoid excessively long or circular lists:

		 */
@@ -88,6 +93,9 @@ void compat_exit_robust_list(struct task_struct *curr) 


		cond_resched();

	}

	if (pending)

		handle_futex_death((void __user *)pending + futex_offset,

				   curr, pip);

}



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