inotify: fix lock ordering wrt do_page_fault's mmap_sem
Fix inotify lock order reversal with mmap_sem due to holding locks over
copy_to_user.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Reported-by: "Daniel J Blueman" <daniel.blueman@gmail.com>
Tested-by: "Daniel J Blueman" <daniel.blueman@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/inotify_user.c b/fs/inotify_user.c
index 6024942..d85c7d9 100644
--- a/fs/inotify_user.c
+++ b/fs/inotify_user.c
@@ -323,7 +323,7 @@
}
/*
- * remove_kevent - cleans up and ultimately frees the given kevent
+ * remove_kevent - cleans up the given kevent
*
* Caller must hold dev->ev_mutex.
*/
@@ -334,7 +334,13 @@
dev->event_count--;
dev->queue_size -= sizeof(struct inotify_event) + kevent->event.len;
+}
+/*
+ * free_kevent - frees the given kevent.
+ */
+static void free_kevent(struct inotify_kernel_event *kevent)
+{
kfree(kevent->name);
kmem_cache_free(event_cachep, kevent);
}
@@ -350,6 +356,7 @@
struct inotify_kernel_event *kevent;
kevent = inotify_dev_get_event(dev);
remove_kevent(dev, kevent);
+ free_kevent(kevent);
}
}
@@ -433,17 +440,15 @@
dev = file->private_data;
while (1) {
- int events;
prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE);
mutex_lock(&dev->ev_mutex);
- events = !list_empty(&dev->events);
- mutex_unlock(&dev->ev_mutex);
- if (events) {
+ if (!list_empty(&dev->events)) {
ret = 0;
break;
}
+ mutex_unlock(&dev->ev_mutex);
if (file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
@@ -462,7 +467,6 @@
if (ret)
return ret;
- mutex_lock(&dev->ev_mutex);
while (1) {
struct inotify_kernel_event *kevent;
@@ -481,6 +485,13 @@
}
break;
}
+ remove_kevent(dev, kevent);
+
+ /*
+ * Must perform the copy_to_user outside the mutex in order
+ * to avoid a lock order reversal with mmap_sem.
+ */
+ mutex_unlock(&dev->ev_mutex);
if (copy_to_user(buf, &kevent->event, event_size)) {
ret = -EFAULT;
@@ -498,7 +509,9 @@
count -= kevent->event.len;
}
- remove_kevent(dev, kevent);
+ free_kevent(kevent);
+
+ mutex_lock(&dev->ev_mutex);
}
mutex_unlock(&dev->ev_mutex);