httpd: reject obs-fold with 400 (RFC 9112 5.2)

Replace silent kv_extend normalisation with an unconditional 400.
RFC 9112 5.2 explicitly permits rejection; it is the safer choice
over SP replacement, which hides parser ambiguity downstream.

Reported by Stuart Thomas, OK kirill@

usr.sbin/httpd/httpd.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: httpd.c,v 1.78 2026/05/11 22:33:10 kirill Exp $	*/
+/*	$OpenBSD: httpd.c,v 1.79 2026/06/03 19:25:06 rsadowski Exp $	*/
 
 /*
  * Copyright (c) 2014 Reyk Floeter <reyk@openbsd.org>
@@ -1023,25 +1023,6 @@ kv_delete(struct kvtree *keys, struct kv *kv)
 	free(kv);
 }
 
-struct kv *
-kv_extend(struct kvtree *keys, struct kv *kv, char *value)
-{
-	char		*newvalue;
-
-	if (kv == NULL) {
-		return (NULL);
-	} else if (kv->kv_value != NULL) {
-		if (asprintf(&newvalue, "%s%s", kv->kv_value, value) == -1)
-			return (NULL);
-
-		free(kv->kv_value);
-		kv->kv_value = newvalue;
-	} else if ((kv->kv_value = strdup(value)) == NULL)
-		return (NULL);
-
-	return (kv);
-}
-
 void
 kv_purge(struct kvtree *keys)
 {

usr.sbin/httpd/httpd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: httpd.h,v 1.173 2026/06/01 09:28:42 claudio Exp $	*/
+/*	$OpenBSD: httpd.h,v 1.174 2026/06/03 19:25:06 rsadowski Exp $	*/
 
 /*
  * Copyright (c) 2006 - 2015 Reyk Floeter <reyk@openbsd.org>
@@ -740,7 +740,6 @@ int		 kv_set(struct kv *, char *, ...)
 int		 kv_setkey(struct kv *, char *, ...)
 		    __attribute__((__format__ (printf, 2, 3)));
 void		 kv_delete(struct kvtree *, struct kv *);
-struct kv	*kv_extend(struct kvtree *, struct kv *, char *);
 void		 kv_purge(struct kvtree *);
 void		 kv_free(struct kv *);
 struct kv	*kv_find(struct kvtree *, struct kv *);

usr.sbin/httpd/server_http.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: server_http.c,v 1.163 2026/06/01 09:28:42 claudio Exp $	*/
+/*	$OpenBSD: server_http.c,v 1.164 2026/06/03 19:25:06 rsadowski Exp $	*/
 
 /*
  * Copyright (c) 2020 Matthias Pressfreund <mpfr@fn.de>
@@ -284,31 +284,22 @@ server_read_http(struct bufferevent *bev, void *arg)
 		 */
 		if (++clt->clt_line == 1)
 			value = strchr(key, ' ');
-		else if (*key == ' ' || *key == '\t')
-			/* Multiline headers wrap with a space or tab */
-			value = NULL;
+		else if (*key == ' ' || *key == '\t') {
+			/*
+			 * RFC 9112 section 5.2 permits unconditional rejection
+			 */
+			server_abort_http(clt, 400, "malformed");
+			goto abort;
+		}
 		else {
-			/* Not a multiline header, should have a : */
 			value = strchr(key, ':');
-			if (value == NULL) {
-				server_abort_http(clt, 400, "malformed");
-				goto abort;
-			}
 		}
+
 		if (value == NULL) {
-			if (clt->clt_line == 1) {
-				server_abort_http(clt, 400, "malformed");
-				goto abort;
-			}
-
-			/* Append line to the last header, if present */
-			if (kv_extend(&desc->http_headers,
-			    desc->http_lastheader, line) == NULL)
-				goto fail;
-
-			free(line);
-			continue;
+			server_abort_http(clt, 400, "malformed");
+			goto abort;
 		}
+
 		if (*value == ':') {
 			*value++ = '\0';
 			value += strspn(value, " \t\r\n");