From 2eebf582c9b3106abb9c33f4fc0a347fb9391037 Mon Sep 17 00:00:00 2001 From: Eric Paris Date: Wed, 18 Aug 2010 12:25:50 -0400 Subject: [PATCH] fanotify: flush outstanding perm requests on group destroy When an fanotify listener is closing it may cause a deadlock between the listener and the original task doing an fs operation. If the original task is waiting for a permissions response it will be holding the srcu lock. The listener cannot clean up and exit until after that srcu lock is syncronized. Thus deadlock. The fix introduced here is to stop accepting new permissions events when a listener is shutting down and to grant permission for all outstanding events. Thus the original task will eventually release the srcu lock and the listener can complete shutdown. Reported-by: Andreas Gruenbacher Cc: Andreas Gruenbacher Signed-off-by: Eric Paris --- fs/notify/fanotify/fanotify_user.c | 27 +++++++++++++++++++++++++++ include/linux/fanotify.h | 7 ------- include/linux/fsnotify_backend.h | 1 + 3 files changed, 28 insertions(+), 7 deletions(-) diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index 032b837fcd11..b966b7230f47 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -195,6 +195,14 @@ static int prepare_for_access_response(struct fsnotify_group *group, re->fd = fd; mutex_lock(&group->fanotify_data.access_mutex); + + if (group->fanotify_data.bypass_perm) { + mutex_unlock(&group->fanotify_data.access_mutex); + kmem_cache_free(fanotify_response_event_cache, re); + event->response = FAN_ALLOW; + return 0; + } + list_add_tail(&re->list, &group->fanotify_data.access_list); mutex_unlock(&group->fanotify_data.access_mutex); @@ -364,9 +372,28 @@ static ssize_t fanotify_write(struct file *file, const char __user *buf, size_t static int fanotify_release(struct inode *ignored, struct file *file) { struct fsnotify_group *group = file->private_data; + struct fanotify_response_event *re, *lre; pr_debug("%s: file=%p group=%p\n", __func__, file, group); +#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS + mutex_lock(&group->fanotify_data.access_mutex); + + group->fanotify_data.bypass_perm = true; + + list_for_each_entry_safe(re, lre, &group->fanotify_data.access_list, list) { + pr_debug("%s: found group=%p re=%p event=%p\n", __func__, group, + re, re->event); + + list_del_init(&re->list); + re->event->response = FAN_ALLOW; + + kmem_cache_free(fanotify_response_event_cache, re); + } + mutex_unlock(&group->fanotify_data.access_mutex); + + wake_up(&group->fanotify_data.access_waitq); +#endif /* matches the fanotify_init->fsnotify_alloc_group */ fsnotify_put_group(group); diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h index f0949a57ca9d..985435622ecd 100644 --- a/include/linux/fanotify.h +++ b/include/linux/fanotify.h @@ -95,11 +95,4 @@ struct fanotify_response { (long)(meta)->event_len >= (long)FAN_EVENT_METADATA_LEN && \ (long)(meta)->event_len <= (long)(len)) -#ifdef __KERNEL__ - -struct fanotify_wait { - struct fsnotify_event *event; - __s32 fd; -}; -#endif /* __KERNEL__ */ #endif /* _LINUX_FANOTIFY_H */ diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h index ed36fb57c426..e40190d16878 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -156,6 +156,7 @@ struct fsnotify_group { struct mutex access_mutex; struct list_head access_list; wait_queue_head_t access_waitq; + bool bypass_perm; /* protected by access_mutex */ #endif /* CONFIG_FANOTIFY_ACCESS_PERMISSIONS */ int f_flags; } fanotify_data; -- 2.20.1