fs/cifs: make share unaccessible at root level mountable

if, when mounting //HOST/share/sub/dir/foo we can query /sub/dir/foo but
not any of the path components above:

- store the /sub/dir/foo prefix in the cifs super_block info
- in the superblock, set root dentry to the subpath dentry (instead of
  the share root)
- set a flag in the superblock to remember it
- use prefixpath when building path from a dentry

fixes bso#8950

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
CC: Stable <stable@vger.kernel.org>
Reviewed-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 49 insertions, 0 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index eb24653612bc..7ae03283bd61 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3485,6 +3485,44 @@ cifs_get_volume_info(char *mount_data, const char *devname)
 	return volume_info;
 }
 
+static int
+cifs_are_all_path_components_accessible(struct TCP_Server_Info *server,
+					unsigned int xid,
+					struct cifs_tcon *tcon,
+					struct cifs_sb_info *cifs_sb,
+					char *full_path)
+{
+	int rc;
+	char *s;
+	char sep, tmp;
+
+	sep = CIFS_DIR_SEP(cifs_sb);
+	s = full_path;
+
+	rc = server->ops->is_path_accessible(xid, tcon, cifs_sb, "");
+	while (rc == 0) {
+		/* skip separators */
+		while (*s == sep)
+			s++;
+		if (!*s)
+			break;
+		/* next separator */
+		while (*s && *s != sep)
+			s++;
+
+		/*
+		 * temporarily null-terminate the path at the end of
+		 * the current component
+		 */
+		tmp = *s;
+		*s = 0;
+		rc = server->ops->is_path_accessible(xid, tcon, cifs_sb,
+						     full_path);
+		*s = tmp;
+	}
+	return rc;
+}
+
 int
 cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *volume_info)
 {
@@ -3622,6 +3660,16 @@ remote_path_check:
 			kfree(full_path);
 			goto mount_fail_check;
 		}
+
+		rc = cifs_are_all_path_components_accessible(server,
+							     xid, tcon, cifs_sb,
+							     full_path);
+		if (rc != 0) {
+			cifs_dbg(VFS, "cannot query dirs between root and final path, "
+				 "enabling CIFS_MOUNT_USE_PREFIX_PATH\n");
+			cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_USE_PREFIX_PATH;
+			rc = 0;
+		}
 		kfree(full_path);
 	}
 
@@ -3891,6 +3939,7 @@ cifs_umount(struct cifs_sb_info *cifs_sb)
 
 	bdi_destroy(&cifs_sb->bdi);
 	kfree(cifs_sb->mountdata);
+	kfree(cifs_sb->prepath);
 	call_rcu(&cifs_sb->rcu, delayed_free);
 }