tls: support specifying accepted TLS ciphers

Introduce a new `-P` option which allows specifying a colon separated list
of accepted TLS ciphers.

Depending on the underlying ustream-ssl provider, the list either follows
OpenSSL's cipher string format or, in case of mbedTLS, is a simple colon
separated cipher whitelist.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

main.c

@@ -139,6 +139,7 @@ static int usage(const char *name)
 		"	-s [addr:]port  Like -p but provide HTTPS on this port\n"
 		"	-C file         ASN.1 server certificate file\n"
 		"	-K file         ASN.1 server private key file\n"
+		"	-P ciphers      Colon separated list of allowed TLS ciphers\n"
 		"	-q              Redirect all HTTP requests to HTTPS\n"
 #endif
 		"	-h directory    Specify the document root, default is '.'\n"
@@ -249,7 +250,7 @@ int main(int argc, char **argv)
 	int bound = 0;
 #ifdef HAVE_TLS
 	int n_tls = 0;
-	const char *tls_key = NULL, *tls_crt = NULL;
+	const char *tls_key = NULL, *tls_crt = NULL, *tls_ciphers = NULL;
 #endif
 #ifdef HAVE_LUA
 	const char *lua_prefix = NULL, *lua_handler = NULL;
@@ -261,7 +262,7 @@ int main(int argc, char **argv)
 	init_defaults_pre();
 	signal(SIGPIPE, SIG_IGN);
 
-	while ((ch = getopt(argc, argv, "A:aC:c:Dd:E:fh:H:I:i:K:k:L:l:m:N:n:p:qRr:Ss:T:t:U:u:Xx:y:")) != -1) {
+	while ((ch = getopt(argc, argv, "A:aC:c:Dd:E:fh:H:I:i:K:k:L:l:m:N:n:P:p:qRr:Ss:T:t:U:u:Xx:y:")) != -1) {
 		switch(ch) {
 #ifdef HAVE_TLS
 		case 'C':
@@ -272,6 +273,10 @@ int main(int argc, char **argv)
 			tls_key = optarg;
 			break;
 
+		case 'P':
+			tls_ciphers = optarg;
+			break;
+
 		case 'q':
 			conf.tls_redirect = 1;
 			break;
@@ -282,6 +287,7 @@ int main(int argc, char **argv)
 #else
 		case 'C':
 		case 'K':
+		case 'P':
 		case 'q':
 		case 's':
 			fprintf(stderr, "uhttpd: TLS support not compiled, "
@@ -523,7 +529,7 @@ int main(int argc, char **argv)
 			return 1;
 		}
 
-		if (uh_tls_init(tls_key, tls_crt))
+		if (uh_tls_init(tls_key, tls_crt, tls_ciphers))
 		    return 1;
 	}
 #endif

tls.c

@@ -31,7 +31,7 @@ static struct ustream_ssl_ops *ops;
 static void *dlh;
 static void *ctx;
 
-int uh_tls_init(const char *key, const char *crt)
+int uh_tls_init(const char *key, const char *crt, const char *ciphers)
 {
 	static bool _init = false;
 
@@ -63,6 +63,11 @@ int uh_tls_init(const char *key, const char *crt)
 		return -EINVAL;
 	}
 
+	if (ciphers && ops->context_set_ciphers(ctx, ciphers)) {
+		fprintf(stderr, "No recognized ciphers in cipher list\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 

tls.h

@@ -22,13 +22,13 @@
 
 #ifdef HAVE_TLS
 
-int uh_tls_init(const char *key, const char *crt);
+int uh_tls_init(const char *key, const char *crt, const char *ciphers);
 void uh_tls_client_attach(struct client *cl);
 void uh_tls_client_detach(struct client *cl);
 
 #else
 
-static inline int uh_tls_init(const char *key, const char *crt)
+static inline int uh_tls_init(const char *key, const char *crt, const char *ciphers)
 {
 	return -1;
 }