inotify: invalid mask should return a error number but not set it

When we run the crackerjack testsuite, the inotify_add_watch test is
stalled.

This is caused by the invalid mask 0 - the task is waiting for the event
but it never comes.  inotify_add_watch() should return -EINVAL as it did
before commit 676a0675cf ("inotify: remove broken mask checks causing
unmount to be EINVAL").  That commit removes the invalid mask check, but
that check is needed.

Check the mask's ALL_INOTIFY_BITS before the inotify_arg_to_mask() call.
If none are set, just return -EINVAL.

Because IN_UNMOUNT is in ALL_INOTIFY_BITS, this change will not trigger
the problem that above commit fixed.

[akpm@linux-foundation.org: fix build]
Signed-off-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
Acked-by: Jim Somerville <Jim.Somerville@windriver.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Eric Paris <eparis@parisplace.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/notify/inotify/inotify_user.c

@@ -570,7 +570,6 @@ static int inotify_update_existing_watch(struct fsnotify_group *group,
 	int add = (arg & IN_MASK_ADD);
 	int ret;
 
-	/* don't allow invalid bits: we don't want flags set */
 	mask = inotify_arg_to_mask(arg);
 
 	fsn_mark = fsnotify_find_inode_mark(group, inode);
@@ -621,7 +620,6 @@ static int inotify_new_watch(struct fsnotify_group *group,
 	struct idr *idr = &group->inotify_data.idr;
 	spinlock_t *idr_lock = &group->inotify_data.idr_lock;
 
-	/* don't allow invalid bits: we don't want flags set */
 	mask = inotify_arg_to_mask(arg);
 
 	tmp_i_mark = kmem_cache_alloc(inotify_inode_mark_cachep, GFP_KERNEL);
@@ -747,6 +745,10 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname,
 	int ret;
 	unsigned flags = 0;
 
+	/* don't allow invalid bits: we don't want flags set */
+	if (unlikely(!(mask & ALL_INOTIFY_BITS)))
+		return -EINVAL;
+
 	f = fdget(fd);
 	if (unlikely(!f.file))
 		return -EBADF;