work around comically tiny HOST_NAME_MAX on glibc system

glibc is clearly violating POSIX since they set HOST_NAME_MAX to 64, and
they've known so for years.  Unfortunately this means that, despite
using the right interfaces, we have to work around bugs in their libc.
ugh.

Luckily, gmid doesn't need to do DNS, it just needs a define large
enough to store a hostname, but not unlimited, to catch possible
misconfigurations.  We don't risk to round-trip this into an interface
that expects smaller strings.

Reported and fix tested by Anna “CyberTailor”,
see <https://codeberg.org/op/gmid/issues/3>.

4 files changed, 24 insertions, 13 deletions

diff --git a/configure b/configure
index 6aa6128..d802484 100755
--- a/configure
+++ b/configure
@@ -644,14 +644,6 @@ cat <<__HEREDOC__
 #  define LOGIN_NAME_MAX 32
 # endif
 #endif
-
-#ifndef HOST_NAME_MAX
-# if defined(_POSIX_HOST_NAME_MAX)
-#  define HOST_NAME_MAX _POSIX_HOST_NAME_MAX
-# else
-#  define HOST_NAME_MAX 255
-# endif
-#endif
 __HEREDOC__
 
 echo "file config.h: written" 1>&2
diff --git a/gmid.h b/gmid.h
index d68e0e3..15f8622 100644
--- a/gmid.h
+++ b/gmid.h
@@ -86,6 +86,15 @@
 
 #define TLS_CERT_HASH_SIZE	128
 
+/*
+ * glibc is violating POSIX by defining HOST_NAME_MAX to a ridicully
+ * small value, so we can't use it.  Luckily, we don't have to do DNS
+ * so we don't risk to pass buffers too big to functions that might
+ * not expect them, we just need a fixed size buffer to catch possible
+ * misconfigurations.
+ */
+#define GMID_HOST_NAME_MAX	255	/* without NUL */
+
 /* forward declaration */
 struct privsep;
 struct privsep_proc;
@@ -144,19 +153,19 @@ struct envlist {
 
 TAILQ_HEAD(aliashead, alist);
 struct alist {
-	char		alias[HOST_NAME_MAX + 1];
+	char		alias[GMID_HOST_NAME_MAX + 1];
 	TAILQ_ENTRY(alist) aliases;
 };
 
 TAILQ_HEAD(proxyhead, proxy);
 struct proxy {
 	char		 match_proto[32];
-	char		 match_host[HOST_NAME_MAX + 1];
+	char		 match_host[GMID_HOST_NAME_MAX + 1];
 	char		 match_port[32];
 
-	char		 host[HOST_NAME_MAX + 1];
+	char		 host[GMID_HOST_NAME_MAX + 1];
 	char		 port[32];
-	char		 sni[HOST_NAME_MAX];
+	char		 sni[GMID_HOST_NAME_MAX];
 	int		 notls;
 	uint32_t	 protocols;
 	int		 noverifyname;
@@ -199,7 +208,7 @@ struct location {
 
 TAILQ_HEAD(vhosthead, vhost);
 struct vhost {
-	char		 domain[HOST_NAME_MAX + 1];
+	char		 domain[GMID_HOST_NAME_MAX + 1];
 	char		*cert_path;
 	char		*key_path;
 	char		*ocsp_path;
diff --git a/regress/regress b/regress/regress
index c3bbed8..1d14644 100755
--- a/regress/regress
+++ b/regress/regress
@@ -40,6 +40,7 @@ run_test test_gemexp
 
 # Run regression tests for the gmid binary.
 run_test test_static_files
+run_test test_alias_long_hostname
 run_test test_directory_redirect
 run_test test_serve_big_files
 run_test test_dont_execute_scripts
diff --git a/regress/tests.sh b/regress/tests.sh
index 0e07d19..4d89c2d 100644
--- a/regress/tests.sh
+++ b/regress/tests.sh
@@ -90,6 +90,15 @@ test_static_files() {
 	check_reply "20 text/gemini" "# hello world" || return 1
 }
 
+test_alias_long_hostname() {
+	setup_simple_test '' '
+alias "laYkH0yyd7xDFO152Ubtm9Efxg8Gvt7wssNd8pPTVIIXVYbYrZERl38LrVY30WbrMrZxLFfhnmsfe1X2FUNAGMVYAxPspjl4"
+'
+
+	fetch /
+	check_reply "20 text/gemini" "# hello world" || return 1
+}
+
 test_directory_redirect() {
 	setup_simple_test