From 5838d4442bd5971687b72221736222637e03140d Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Wed, 6 Aug 2014 16:03:28 -0700 Subject: fanotify: fix double free of pending permission events Commit 85816794240b ("fanotify: Fix use after free for permission events") introduced a double free issue for permission events which are pending in group's notification queue while group is being destroyed. These events are freed from fanotify_handle_event() but they are not removed from groups notification queue and thus they get freed again from fsnotify_flush_notify(). Fix the problem by removing permission events from notification queue before freeing them if we skip processing access response. Also expand comments in fanotify_release() to explain group shutdown in detail. Fixes: 85816794240b9659e66e4d9b0df7c6e814e5f603 Signed-off-by: Jan Kara Reported-by: Douglas Leeder Tested-by: Douglas Leeder Reported-by: Heinrich Schuchard Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/notify/fanotify/fanotify.c | 9 ++++++++- fs/notify/fanotify/fanotify_user.c | 12 ++++++++++++ 2 files changed, 20 insertions(+), 1 deletion(-) (limited to 'fs/notify/fanotify') diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c index fdeb36b70c65..30d3addfad75 100644 --- a/fs/notify/fanotify/fanotify.c +++ b/fs/notify/fanotify/fanotify.c @@ -70,8 +70,15 @@ static int fanotify_get_response(struct fsnotify_group *group, wait_event(group->fanotify_data.access_waitq, event->response || atomic_read(&group->fanotify_data.bypass_perm)); - if (!event->response) /* bypass_perm set */ + if (!event->response) { /* bypass_perm set */ + /* + * Event was canceled because group is being destroyed. Remove + * it from group's event list because we are responsible for + * freeing the permission event. + */ + fsnotify_remove_event(group, &event->fae.fse); return 0; + } /* userspace responded, convert to something usable */ switch (event->response) { diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index fbf2210823ab..b13992a41bd9 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -359,6 +359,11 @@ static int fanotify_release(struct inode *ignored, struct file *file) #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS struct fanotify_perm_event_info *event, *next; + /* + * There may be still new events arriving in the notification queue + * but since userspace cannot use fanotify fd anymore, no event can + * enter or leave access_list by now. + */ spin_lock(&group->fanotify_data.access_lock); atomic_inc(&group->fanotify_data.bypass_perm); @@ -373,6 +378,13 @@ static int fanotify_release(struct inode *ignored, struct file *file) } spin_unlock(&group->fanotify_data.access_lock); + /* + * Since bypass_perm is set, newly queued events will not wait for + * access response. Wake up the already sleeping ones now. + * synchronize_srcu() in fsnotify_destroy_group() will wait for all + * processes sleeping in fanotify_handle_event() waiting for access + * response and thus also for all permission events to be freed. + */ wake_up(&group->fanotify_data.access_waitq); #endif -- cgit v1.2.3