shared: fix handling of suffix "." in dns_name_compare_func()

All our other domain name handling functions make no destinction between
domain names that end in a dot plus a NUL, or those just ending in a
NUL. Make sure dns_name_compare_func() and dns_label_unescape_suffix()
do the same.

2 files changed, 27 insertions, 9 deletions

diff --git a/src/shared/dns-domain.c b/src/shared/dns-domain.c
index 159944858d..0273b9e3c9 100644
--- a/src/shared/dns-domain.c
+++ b/src/shared/dns-domain.c
@@ -154,20 +154,24 @@ int dns_label_unescape_suffix(const char *name, const char **label_terminal, cha
                 return 0;
         }
 
-        assert(**label_terminal == '.' || **label_terminal == 0);
+        terminal = *label_terminal;
+        assert(*terminal == '.' || *terminal == 0);
 
-        /* skip current terminal character */
-        terminal = *label_terminal - 1;
+        /* Skip current terminal character (and accept domain names ending it ".") */
+        if (*terminal == 0)
+                terminal--;
+        if (terminal >= name && *terminal == '.')
+                terminal--;
 
-        /* point name to the last label, and terminal to the preceding terminal symbol (or make it a NULL pointer) */
+        /* Point name to the last label, and terminal to the preceding terminal symbol (or make it a NULL pointer) */
         for (;;) {
                 if (terminal < name) {
-                        /* reached the first label, so indicate that there are no more */
+                        /* Reached the first label, so indicate that there are no more */
                         terminal = NULL;
                         break;
                 }
 
-                /* find the start of the last label */
+                /* Find the start of the last label */
                 if (*terminal == '.') {
                         const char *y;
                         unsigned slashes = 0;
@@ -176,7 +180,7 @@ int dns_label_unescape_suffix(const char *name, const char **label_terminal, cha
                                 slashes ++;
 
                         if (slashes % 2 == 0) {
-                                /* the '.' was not escaped */
+                                /* The '.' was not escaped */
                                 name = terminal + 1;
                                 break;
                         } else {
diff --git a/src/test/test-dns-domain.c b/src/test/test-dns-domain.c
index 78c5631ff1..1b0cb153f7 100644
--- a/src/test/test-dns-domain.c
+++ b/src/test/test-dns-domain.c
@@ -140,9 +140,9 @@ static void test_dns_label_unescape_suffix(void) {
         test_dns_label_unescape_suffix_one("hallo\\", "hallo", "hallo", 20, -EINVAL, -EINVAL);
         test_dns_label_unescape_suffix_one("hallo\\032 ", "hallo  ", "", 20, 7, 0);
         test_dns_label_unescape_suffix_one(".", "", "", 20, 0, 0);
-        test_dns_label_unescape_suffix_one("..", "", "", 20, 0, 0);
+        test_dns_label_unescape_suffix_one("..", "", "", 20, 0, -EINVAL);
         test_dns_label_unescape_suffix_one(".foobar", "foobar", "", 20, 6, -EINVAL);
-        test_dns_label_unescape_suffix_one("foobar.", "", "foobar", 20, 0, 6);
+        test_dns_label_unescape_suffix_one("foobar.", "foobar", "", 20, 6, 0);
         test_dns_label_unescape_suffix_one("foo\\\\bar", "foo\\bar", "", 20, 7, 0);
         test_dns_label_unescape_suffix_one("foo.bar", "bar", "foo", 20, 3, 3);
         test_dns_label_unescape_suffix_one("foo..bar", "bar", "", 20, 3, -EINVAL);
@@ -546,6 +546,19 @@ static void test_dns_name_equal_skip(void) {
         test_dns_name_equal_skip_one("", 2, "foo", 0);
 }
 
+static void test_dns_name_compare_func(void) {
+        assert_se(dns_name_compare_func("", "") == 0);
+        assert_se(dns_name_compare_func("", ".") == 0);
+        assert_se(dns_name_compare_func(".", "") == 0);
+        assert_se(dns_name_compare_func("foo", "foo.") == 0);
+        assert_se(dns_name_compare_func("foo.", "foo") == 0);
+        assert_se(dns_name_compare_func("foo", "foo") == 0);
+        assert_se(dns_name_compare_func("foo.", "foo.") == 0);
+        assert_se(dns_name_compare_func("heise.de", "HEISE.DE.") == 0);
+
+        assert_se(dns_name_compare_func("de.", "heise.de") != 0);
+}
+
 int main(int argc, char *argv[]) {
 
         test_dns_label_unescape();
@@ -569,6 +582,7 @@ int main(int argc, char *argv[]) {
         test_dns_name_suffix();
         test_dns_name_count_labels();
         test_dns_name_equal_skip();
+        test_dns_name_compare_func();
 
         return 0;
 }