resolv: ns_name_pton should report trailing \ as error [BZ #22413]

Author: fweimer-rh

ChangeLog

@@ -1,3 +1,9 @@
+2017-11-11  Florian Weimer  <[email protected]>
+
+	[BZ #22413]
+	* resolv/ns_name.c (ns_name_pton): Treat trailing backslash as error.
+	* resolv/tst-ns_name_pton.c (tests): Add trailing backslash tests.
+
 2017-11-11  Florian Weimer  <[email protected]>
 
 	* resolv/tst-ns_name_pton.c: New file.

resolv/ns_name.c

@@ -222,6 +222,11 @@ ns_name_pton(const char *src, u_char *dst, size_t dstsiz)
 		}
 		*bp++ = (u_char)c;
 	}
+	if (escaped) {
+		/* Trailing backslash.  */
+		__set_errno (EMSGSIZE);
+		return -1;
+	}
 	c = (bp - label - 1);
 	if ((c & NS_CMPRSFLGS) != 0) {		/*%< Label too big. */
 		__set_errno (EMSGSIZE);

resolv/tst-ns_name_pton.c

@@ -127,6 +127,13 @@ static const struct test_case tests[] =
       "\377\377", NULL, },
     { STRING63OCT "." STRING63OCT "." STRING63OCT "." STRING60OCT
       "\377\377\377", NULL, },
+    { "\\", NULL, },
+    { "\\\\", "\\\\", false },
+    { "\\\\.", "\\\\", true },
+    { "\\\\\\", NULL, },
+    { "a\\", NULL, },
+    { "a.\\", NULL, },
+    { "a.b\\", NULL, },
   };
 
 static int