knfsd: Validate filehandle type in fsid_source

fsid_source decided where to get the 'fsid' number to
return for a GETATTR based on the type of filehandle.
It can be from the device, from the fsid, or from the
UUID.

It is possible for the filehandle to be inconsistent
with the export information, so make sure the export information
actually has the info implied by the value returned by
fsid_source.

Signed-off-by: Neil Brown <[e-mail]>
Cc: "Luiz Fernando N. Capitulino" <[e-mail]>
Signed-off-by: "J. Bruce Fields" <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/nfsd/nfsfh.c

···
 	case FSID_DEV:
 	case FSID_ENCODE_DEV:
 	case FSID_MAJOR_MINOR:
-		return FSIDSOURCE_DEV;
+		if (fhp->fh_export->ex_dentry->d_inode->i_sb->s_type->fs_flags
+		    & FS_REQUIRES_DEV)
+			return FSIDSOURCE_DEV;
+		break;
 	case FSID_NUM:
-		return FSIDSOURCE_FSID;
-	default:
 		if (fhp->fh_export->ex_flags & NFSEXP_FSID)
 			return FSIDSOURCE_FSID;
-		else
-			return FSIDSOURCE_UUID;
+		break;
+	default:
+		break;
 	}
+	/* either a UUID type filehandle, or the filehandle doesn't
+	 * match the export.
+	 */
+	if (fhp->fh_export->ex_flags & NFSEXP_FSID)
+		return FSIDSOURCE_FSID;
+	if (fhp->fh_export->ex_uuid)
+		return FSIDSOURCE_UUID;
+	return FSIDSOURCE_DEV;
 }