inotify: Ensure we alwasy write the terminating NULL.

Before the rewrite copy_event_to_user always wrote a terqminating '\0'
byte to user space after the filename.  Since the rewrite that
terminating byte was skipped if your filename is exactly a multiple of
event_size.  Ouch!

So add one byte to name_size before we round up and use clear_user to
set userspace to zero like /dev/zero does instead of copying the
strange nul_inotify_event.  I can't quite convince myself len_to_zero
will never exceed 16 and even if it doesn't clear_user should be more
efficient and a more accurate reflection of what the code is trying to
do.

Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index ce1f5823e2c2..0e781bc88d1e 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -47,9 +47,6 @@
 
 static struct vfsmount *inotify_mnt __read_mostly;
 
-/* this just sits here and wastes global memory.  used to just pad userspace messages with zeros */
-static struct inotify_event nul_inotify_event;
-
 /* these are configurable via /proc/sys/fs/inotify/ */
 static int inotify_max_user_instances __read_mostly;
 static int inotify_max_queued_events __read_mostly;
@@ -199,8 +196,10 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
                 inotify_free_event_priv(fsn_priv);
         }
 
-        /* round up event->name_len so it is a multiple of event_size */
-        name_len = roundup(event->name_len, event_size);
+        /* round up event->name_len so it is a multiple of event_size
+         * plus an extra byte for the terminating '\0'.
+         */
+        name_len = roundup(event->name_len + 1, event_size);
         inotify_event.len = name_len;
 
         inotify_event.mask = inotify_mask_to_arg(event->mask);
@@ -224,8 +223,8 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
                         return -EFAULT;
                 buf += event->name_len;
 
-                /* fill userspace with 0's from nul_inotify_event */
-                if (copy_to_user(buf, &nul_inotify_event, len_to_zero))
+                /* fill userspace with 0's */
+                if (clear_user(buf, len_to_zero))
                         return -EFAULT;
                 buf += len_to_zero;
                 event_size += name_len;