fsnotify: fix oops in fsnotify_clear_marks_by_group_flags() (8f2f3eb5) · Commits · 戴 / test

fsnotify_clear_marks_by_group_flags() can race with fsnotify_destroy_marks() so that when fsnotify_destroy_mark_locked() drops mark_mutex, a mark from the list iterated by fsnotify_clear_marks_by_group_flags() can be freed and thus the next entry pointer we have cached may become stale and we dereference free memory. Fix the problem by first moving marks to free to a special private list and then always free the first entry in the special list. This method is safe even when entries from the list can disappear once we drop the lock. Signed-off-by:

Jan Kara <jack@suse.com> Reported-by:

Ashish Sangwan <a.sangwan@samsung.com> Reviewed-by:

Ashish Sangwan <a.sangwan@samsung.com> Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de> Cc: <stable@vger.kernel.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/notify/mark.c

+25 −5

Original line number	Diff line number	Diff line
		@@ -412,17 +412,37 @@ void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
		unsigned int flags)
		{
		struct fsnotify_mark lmark, mark;
		LIST_HEAD(to_free);

		/*
		* We have to be really careful here. Anytime we drop mark_mutex, e.g.
		* fsnotify_clear_marks_by_inode() can come and free marks. Even in our
		* to_free list so we have to use mark_mutex even when accessing that
		* list. And freeing mark requires us to drop mark_mutex. So we can
		* reliably free only the first mark in the list. That's why we first
		* move marks to free to to_free list in one go and then free marks in
		* to_free list one by one.
		*/
		mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
		list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
		if (mark->flags & flags) {
		if (mark->flags & flags)
		list_move(&mark->g_list, &to_free);
		}
		mutex_unlock(&group->mark_mutex);

		while (1) {
		mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
		if (list_empty(&to_free)) {
		mutex_unlock(&group->mark_mutex);
		break;
		}
		mark = list_first_entry(&to_free, struct fsnotify_mark, g_list);
		fsnotify_get_mark(mark);
		fsnotify_destroy_mark_locked(mark, group);
		mutex_unlock(&group->mark_mutex);
		fsnotify_put_mark(mark);
		}
		}
		mutex_unlock(&group->mark_mutex);
		}

		/*
		* Given a group, destroy all of the marks associated with that group.

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