BZ#16469: resolv: skip leading dot in domain to search

This should only happen if the domain to search is the root,
represented as "." rather than by an empty string.  Skipping it here
prevents libc_res_nquerydomain from duplicating the trailing dot,
which would cause the domain name compression to fail.

for  ChangeLog

	[BZ #16469]
	* resolv/res_query.c (__libc_res_nsearch): Skip leading dot in
	search domain names.

ChangeLog

@@ -1,3 +1,9 @@
+2014-11-21  Alexandre Oliva <aoliva@redhat.com>
+
+	[BZ #16469]
+	* resolv/res_query.c (__libc_res_nsearch): Skip leading dot in
+	search domain names.
+
 2014-11-21  Alexandre Oliva <aoliva@redhat.com>
 
 	[BZ #16469]

resolv/res_query.c

@@ -413,13 +413,24 @@ __libc_res_nsearch(res_state statp,
 		for (domain = (const char * const *)statp->dnsrch;
 		     *domain && !done;
 		     domain++) {
+			const char *dname = domain[0];
 			searched = 1;
 
-			if (domain[0][0] == '\0' ||
-			    (domain[0][0] == '.' && domain[0][1] == '\0'))
+			/* __libc_res_nquerydoman concatenates name
+			   with dname with a "." in between.  If we
+			   pass it in dname the "." we got from the
+			   configured default search path, we'll end
+			   up with "name..", which won't resolve.
+			   OTOH, passing it "" will result in "name.",
+			   which has the intended effect for both
+			   possible representations of the root
+			   domain.  */
+			if (dname[0] == '.')
+				dname++;
+			if (dname[0] == '\0')
 				root_on_list++;
 
-			ret = __libc_res_nquerydomain(statp, name, *domain,
+			ret = __libc_res_nquerydomain(statp, name, dname,
 						      class, type,
 						      answer, anslen, answerp,
 						      answerp2, nanswerp2,