fanotify: hooks the fanotify_mark syscall to the vfsmount code

Create a new fanotify_mark flag which indicates we should attach the mark
to the vfsmount holding the object referenced by dfd and pathname rather
than the inode itself.
Signed-off-by: Eric Paris <eparis@redhat.com>

fs/notify/fanotify/fanotify_user.c

@@ -485,7 +485,8 @@ SYSCALL_DEFINE(fanotify_mark)(int fanotify_fd, unsigned int flags,
 			      __u64 mask, int dfd,
 			      const char  __user * pathname)
 {
-	struct inode *inode;
+	struct inode *inode = NULL;
+	struct vfsmount *mnt = NULL;
 	struct fsnotify_group *group;
 	struct file *filp;
 	struct path path;
@@ -515,16 +516,22 @@ SYSCALL_DEFINE(fanotify_mark)(int fanotify_fd, unsigned int flags,
 		goto fput_and_out;
 
 	/* inode held in place by reference to path; group by fget on fd */
-	inode = path.dentry->d_inode;
+	if (!(flags & FAN_MARK_ON_VFSMOUNT))
+		inode = path.dentry->d_inode;
+	else
+		mnt = path.mnt;
 	group = filp->private_data;
 
 	/* create/update an inode mark */
 	switch (flags & (FAN_MARK_ADD | FAN_MARK_REMOVE)) {
 	case FAN_MARK_ADD:
-		ret = fanotify_add_inode_mark(group, inode, mask);
+		if (flags & FAN_MARK_ON_VFSMOUNT)
+			ret = fanotify_add_vfsmount_mark(group, mnt, mask);
+		else
+			ret = fanotify_add_inode_mark(group, inode, mask);
 		break;
 	case FAN_MARK_REMOVE:
-		ret = fanotify_remove_mark(group, inode, NULL, mask);
+		ret = fanotify_remove_mark(group, inode, mnt, mask);
 		break;
 	default:
 		ret = -EINVAL;

include/linux/fanotify.h

@@ -29,11 +29,13 @@
 #define FAN_MARK_REMOVE		0x00000002
 #define FAN_MARK_DONT_FOLLOW	0x00000004
 #define FAN_MARK_ONLYDIR	0x00000008
+#define FAN_MARK_ON_VFSMOUNT	0x00000010
 
 #define FAN_ALL_MARK_FLAGS	(FAN_MARK_ADD |\
 				 FAN_MARK_REMOVE |\
 				 FAN_MARK_DONT_FOLLOW |\
-				 FAN_MARK_ONLYDIR)
+				 FAN_MARK_ONLYDIR |\
+				 FAN_MARK_ON_VFSMOUNT)
 
 /*
  * All of the events - we build the list by hand so that we can add flags in