dhcp: enforce MUD URL to use "https://" scheme

nm_sd_http_url_is_valid_https() is rather clunky, but it is
this way, because we must not disagree with systemd code
about what makes a valid URL.

RFC 8520 says "MUD URLs MUST use the "https" scheme".

See-also: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/463#note_476190

Fixes: cedcea5ee812 ('libnm: fix verification of connection:mud-url property')

2 files changed, 18 insertions, 13 deletions

diff --git a/shared/systemd/nm-sd-utils-shared.c b/shared/systemd/nm-sd-utils-shared.c
index b4e017c94b..4444e6c7f6 100644
--- a/shared/systemd/nm-sd-utils-shared.c
+++ b/shared/systemd/nm-sd-utils-shared.c
@@ -99,13 +99,14 @@ gboolean nm_sd_hostname_is_valid (const char *s, bool allow_trailing_dot)
 /*****************************************************************************/
 
 static gboolean
-_http_url_is_valid (const char *url)
+_http_url_is_valid (const char *url, gboolean only_https)
 {
 	if (   !url
 	    || !url[0])
 		return FALSE;
 
-	if (NM_STR_HAS_PREFIX (url, "http://"))
+	if (   !only_https
+	    && NM_STR_HAS_PREFIX (url, "http://"))
 		url += NM_STRLEN ("http://");
 	else if (NM_STR_HAS_PREFIX (url, "https://"))
 		url += NM_STRLEN ("https://");
@@ -119,16 +120,20 @@ _http_url_is_valid (const char *url)
 }
 
 gboolean
-nm_sd_http_url_is_valid (const char *url)
+nm_sd_http_url_is_valid_https (const char *url)
 {
-	gboolean v;
-
-	/* http_url_is_valid() is part of our API, as we use it to validate connection
-	 * properties. That means, it's behavior must remain stable (or only change
-	 * with care).
+	/* We use this function to verify connection:mud-url property, it must thus
+	 * not change behavior.
+	 *
+	 * Note that sd_dhcp_client_set_mud_url() and sd_dhcp6_client_set_request_mud_url()
+	 * assert with http_url_is_valid() that the argument is valid. We thus must make
+	 * sure to only pass URLs that are valid according to http_url_is_valid().
+	 *
+	 * This is given, because our nm_sd_http_url_is_valid_https() is more strict
+	 * than http_url_is_valid().
 	 *
-	 * Thus, reimplement it, and make sure that our implementation agrees. */
-	v = _http_url_is_valid (url);
-	nm_assert (v == http_url_is_valid (url));
-	return v;
+	 * We only must make sure that this is also correct in the future, when we
+	 * re-import systemd code. */
+	nm_assert (_http_url_is_valid (url, FALSE) == http_url_is_valid (url));
+	return _http_url_is_valid (url, TRUE);
 }
diff --git a/shared/systemd/nm-sd-utils-shared.h b/shared/systemd/nm-sd-utils-shared.h
index 382db278d1..a3ca1edc03 100644
--- a/shared/systemd/nm-sd-utils-shared.h
+++ b/shared/systemd/nm-sd-utils-shared.h
@@ -36,6 +36,6 @@ gboolean nm_sd_hostname_is_valid(const char *s, bool allow_trailing_dot);
 
 /*****************************************************************************/
 
-gboolean nm_sd_http_url_is_valid (const char *url);
+gboolean nm_sd_http_url_is_valid_https (const char *url);
 
 #endif /* __NM_SD_UTILS_SHARED_H__ */