backport path unmount

Signed-off-by: xenxynon <flynryder427@gmail.com>

fs/internal.h

@@ -85,6 +85,7 @@ extern int finish_automount(struct vfsmount *, struct path *);
 extern int sb_prepare_remount_readonly(struct super_block *);
 
 extern void __init mnt_init(void);
+int path_umount(struct path *path, int flags);
 
 extern int __mnt_want_write_file(struct file *);
 extern void __mnt_drop_write_file(struct file *);

fs/namespace.c

@@ -1750,6 +1750,36 @@ SYSCALL_DEFINE1(oldumount, char __user *, name)
 
 #endif
 
+static int can_umount(const struct path *path, int flags)
+ {
+	 struct mount *mnt = real_mount(path->mnt);
+	 if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
+		 return -EINVAL;
+	 if (!may_mount())
+		 return -EPERM;
+	 if (path->dentry != path->mnt->mnt_root)
+		 return -EINVAL;
+	 if (!check_mnt(mnt))
+		 return -EINVAL;
+	 if (mnt->mnt.mnt_flags & MNT_LOCKED)
+		 return -EINVAL;
+	 if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
+		 return -EPERM;
+	 return 0;
+ }
+
+int path_umount(struct path *path, int flags)
+ {
+	 struct mount *mnt = real_mount(path->mnt);
+	 int ret;
+	 ret = can_umount(path, flags);
+	 if (!ret)
+		 ret = do_umount(mnt, flags);
+	 dput(path->dentry);
+	 mntput_no_expire(mnt);
+	 return ret;
+ }
+
 static bool is_mnt_ns_file(struct dentry *dentry)
 {
 	/* Is this a proxy for a mount namespace? */