From: Aki Tuomi <aki.tuomi@open-xchange.com>
Date: Mon, 17 Apr 2023 05:12:39 +0000 (+0300)
Subject: lib: connection - Add connection_is_valid_dns_name()
X-Git-Tag: 2.4.0~2142
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=26da32a340ff4c92dafb3e764d355fefa6f2af03;p=thirdparty%2Fdovecot%2Fcore.git

lib: connection - Add connection_is_valid_dns_name()

Checks that given name is valid DNS servername, including
characters _ and RFC5891 section 4.2.1 specified ones.
---

diff --git a/src/lib/connection.c b/src/lib/connection.c
index 1897b6e300..41307e2c13 100644
--- a/src/lib/connection.c
+++ b/src/lib/connection.c
@@ -1011,3 +1011,21 @@ void connection_list_deinit(struct connection_list **_list)
 	}
 	i_free(list);
 }
+
+bool connection_is_valid_dns_name(const char *name)
+{
+	const char *p = name;
+	if (*name == '\0')
+		return FALSE;
+	if (strstr(name, "..") != NULL)
+		return FALSE;
+	for (; *p != '\0'; p++) {
+		if ((*p < '0' || *p > '9') &&
+		    (*p < 'A' || *p > 'Z') &&
+		    (*p < 'a' || *p > 'z') &&
+		    *p != '.' && *p != '-' &&
+		    *p != '_' && *p != ':')
+			return FALSE;
+	}
+	return p - name < 256; /* maximum length is 255 by RFC 952 */
+}
diff --git a/src/lib/connection.h b/src/lib/connection.h
index 8318dbf83c..7a0bc10482 100644
--- a/src/lib/connection.h
+++ b/src/lib/connection.h
@@ -275,4 +275,10 @@ int connection_input_line_default(struct connection *conn, const char *line);
 void connection_set_handlers(struct connection *conn, const struct connection_vfuncs *vfuncs);
 void connection_set_default_handlers(struct connection *conn);
 
+/* Checks if the given name is a valid DNS servername as per RFC1123 section 1.2,
+   RFC8591 section 4.2.1 and for practicality, the '_' character.
+   IP address like values are also accepted.
+*/
+bool connection_is_valid_dns_name(const char *name);
+
 #endif
diff --git a/src/lib/test-connection.c b/src/lib/test-connection.c
index feb1f9ceea..b30dc6b40e 100644
--- a/src/lib/test-connection.c
+++ b/src/lib/test-connection.c
@@ -725,6 +725,60 @@ static void test_connection_no_version(void)
 
 /* END NO VERSION TEST */
 
+static void test_connection_is_valid_dns_name(void)
+{
+	test_begin("connection is valid DNS name");
+
+	struct test_case {
+		const char *input;
+		bool valid;
+	} test_cases[] = {
+		{ "", FALSE }, /* empty string is not valid */
+		{ "valid.hostname", TRUE },
+		{ "xn--land-poa.island", TRUE },
+		{ "dns_server.name", TRUE },
+		{ "127.0.0.1", TRUE },
+		{ "fe80::1", TRUE },
+		{ "hello world domain", FALSE }, /* spaces are not valid */
+		{ "hello\tworld\tdomain", FALSE }, /* tabs are not valid */
+		{ "hello,world,domain", FALSE }, /* commas are not valid */
+		{ "hello..world..domain", FALSE }, /* double-dot is not valid */
+		{ "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+		  "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+		  "xxxxxxx.yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
+		  "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
+		  "yyyyyyyyyyyyyyy", TRUE }, /* 255 bytes long */
+		{ "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+		  "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+		  "xxxxxxxx.yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
+		  "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
+		  "yyyyyyyyyyyyyyyy", FALSE }, /* 256 bytes long */
+	};
+
+	/* first, ensure everything not allowed is rejected as first byte. */
+	for (int c = 0; c <= UCHAR_MAX; c++) T_BEGIN {
+		bool valid = TRUE;
+		/* is it valid? */
+		if ((c < '0' || c > '9') &&
+		    (c < 'A' || c > 'Z') &&
+		    (c < 'a' || c > 'z') &&
+		    c != '.' && c != '-' &&
+		    c != '_' && c != ':')
+			valid = FALSE;
+
+		const char *name = t_strdup_printf("%c", (unsigned char)c);
+		test_assert(connection_is_valid_dns_name(name) == valid);
+	} T_END;
+
+	/* then test special cases */
+	for (size_t i = 0; i < N_ELEMENTS(test_cases); i++) {
+		const struct test_case *tc = &test_cases[i];
+		test_assert_idx(connection_is_valid_dns_name(tc->input) == tc->valid, i);
+	}
+
+	test_end();
+}
+
 void test_connection(void)
 {
 	test_connection_simple();
@@ -741,4 +795,5 @@ void test_connection(void)
 	test_connection_handshake_failed_input();
 	test_connection_input_error_reason();
 	test_connection_no_version();
+	test_connection_is_valid_dns_name();
 }