From: Jan Kara <[email protected]> This patch has been added to the 3.18 stable tree. If you have any objections, please let us know.
=============== [ Upstream commit 8f2f3eb59dff4ec538de55f2e0592fec85966aab ] 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 <[email protected]> Reported-by: Ashish Sangwan <[email protected]> Reviewed-by: Ashish Sangwan <[email protected]> Cc: Lino Sanfilippo <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Sasha Levin <[email protected]> --- fs/notify/mark.c | 30 +++++++++++++++++++++++++----- 1 file changed, 25 insertions(+), 5 deletions(-) diff --git a/fs/notify/mark.c b/fs/notify/mark.c index 34c38fa..28c90a6 100644 --- a/fs/notify/mark.c +++ b/fs/notify/mark.c @@ -329,16 +329,36 @@ 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) { - fsnotify_get_mark(mark); - fsnotify_destroy_mark_locked(mark, group); - fsnotify_put_mark(mark); - } + 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); + } } /* -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
