smb: cilent: set reparse mount points as automounts

By doing so we can selectively mark those submounts as 'noserverino'
rather than whole mount and thus avoiding inode collisions in them.

Consider a "test" SMB share that has two mounted NTFS volumes
(vol0 & vol1) inside it.

* Before patch

$ mount.cifs //srv/test /mnt/1 -o ...,serverino
$ ls -li /mnt/1/vol0
total 1
281474976710693 drwxr-xr-x 2 root root 0 Jul 15 00:23 $RECYCLE.BIN
281474976710696 drwxr-xr-x 2 root root 0 Jul 18 18:23 System Volume...
281474976710699 -rwxr-xr-x 1 root root 0 Aug 14 21:53 f0
281474976710700 -rwxr-xr-x 1 root root 0 Aug 15 18:52 f2
281474976710698 drwxr-xr-x 2 root root 0 Aug 12 19:39 foo
281474976710692 -rwxr-xr-x 1 root root 5 Aug  4 21:18 vol0_f0.txt
$ ls -li /mnt/1/vol1
total 0
281474976710693 drwxr-xr-x 2 root root 0 Jul 15 00:23 $RECYCLE.BIN
281474976710696 drwxr-xr-x 2 root root 0 Jul 18 18:23 System Volume...
281474976710698 drwxr-xr-x 2 root root 0 Aug 12 19:39 bar
281474976710699 -rwxr-xr-x 1 root root 0 Aug 14 22:03 f0
281474976710700 -rwxr-xr-x 1 root root 0 Aug 14 22:52 f1
281474976710692 -rwxr-xr-x 1 root root 0 Jul 15 00:23 vol1_f0.txt

* After patch

$ mount.cifs //srv/test /mnt/1 -o ...,serverino
$ ls -li /mnt/1/vol0
total 1
590 drwxr-xr-x 2 root root 0 Jul 15 00:23 $RECYCLE.BIN
594 drwxr-xr-x 2 root root 0 Jul 18 18:23 System Volume Information
591 -rwxr-xr-x 1 root root 0 Aug 14 21:53 f0
592 -rwxr-xr-x 1 root root 0 Aug 15 18:52 f2
593 drwxr-xr-x 2 root root 0 Aug 12 19:39 foo
595 -rwxr-xr-x 1 root root 5 Aug  4 21:18 vol0_f0.txt
$ ls -li /mnt/1/vol1
total 0
596 drwxr-xr-x 2 root root 0 Jul 15 00:23 $RECYCLE.BIN
600 drwxr-xr-x 2 root root 0 Jul 18 18:23 System Volume Information
597 drwxr-xr-x 2 root root 0 Aug 12 19:39 bar
598 -rwxr-xr-x 1 root root 0 Aug 14 22:03 f0
599 -rwxr-xr-x 1 root root 0 Aug 14 22:52 f1
601 -rwxr-xr-x 1 root root 0 Jul 15 00:23 vol1_f0.txt
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/cifsglob.h

@@ -1094,7 +1094,7 @@ cap_unix(struct cifs_ses *ses)
  * inode with new info
  */
 
-#define CIFS_FATTR_DFS_REFERRAL		0x1
+#define CIFS_FATTR_JUNCTION		0x1
 #define CIFS_FATTR_DELETE_PENDING	0x2
 #define CIFS_FATTR_NEED_REVAL		0x4
 #define CIFS_FATTR_INO_COLLISION	0x8

fs/smb/client/namespace.c

@@ -126,9 +126,11 @@ static char *automount_fullpath(struct dentry *dentry, void *page)
 	char *s;
 
 	spin_lock(&tcon->tc_lock);
-	if (unlikely(!tcon->origin_fullpath)) {
+	if (!tcon->origin_fullpath) {
 		spin_unlock(&tcon->tc_lock);
-		return ERR_PTR(-EREMOTE);
+		return build_path_from_dentry_optional_prefix(dentry,
+							      page,
+							      true);
 	}
 	spin_unlock(&tcon->tc_lock);
 
@@ -162,7 +164,6 @@ static struct vfsmount *cifs_do_automount(struct path *path)
 	int rc;
 	struct dentry *mntpt = path->dentry;
 	struct fs_context *fc;
-	struct cifs_sb_info *cifs_sb;
 	void *page = NULL;
 	struct smb3_fs_context *ctx, *cur_ctx;
 	struct smb3_fs_context tmp;
@@ -172,17 +173,7 @@ static struct vfsmount *cifs_do_automount(struct path *path)
 	if (IS_ROOT(mntpt))
 		return ERR_PTR(-ESTALE);
 
-	/*
-	 * The MSDFS spec states that paths in DFS referral requests and
-	 * responses must be prefixed by a single '\' character instead of
-	 * the double backslashes usually used in the UNC. This function
-	 * gives us the latter, so we must adjust the result.
-	 */
-	cifs_sb = CIFS_SB(mntpt->d_sb);
-	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS)
-		return ERR_PTR(-EREMOTE);
-
-	cur_ctx = cifs_sb->ctx;
+	cur_ctx = CIFS_SB(mntpt->d_sb)->ctx;
 
 	fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, mntpt);
 	if (IS_ERR(fc))

fs/smb/client/readdir.c

@@ -143,6 +143,7 @@ static bool reparse_file_needs_reval(const struct cifs_fattr *fattr)
 	case IO_REPARSE_TAG_DFSR:
 	case IO_REPARSE_TAG_SYMLINK:
 	case IO_REPARSE_TAG_NFS:
+	case IO_REPARSE_TAG_MOUNT_POINT:
 	case 0:
 		return true;
 	}