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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.

No testcase for this one; we can't really exercise this in a controlled
fashion without overriding /etc/resolv.conf.

No regressions on x86_64-linux-gnu.  Ok to install?

for  ChangeLog

	[BZ #16469]
	* resolv/res_query.c (__libc_res_nsearch): Skip leading dot in
	search domain names.
 resolv/res_query.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/resolv/res_query.c b/resolv/res_query.c
index 338ad82..0d276b0 100644
--- a/resolv/res_query.c
+++ b/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')
-			ret = __libc_res_nquerydomain(statp, name, *domain,
+			ret = __libc_res_nquerydomain(statp, name, dname,
 						      class, type,
 						      answer, anslen, answerp,
 						      answerp2, nanswerp2,

Alexandre Oliva, freedom fighter
You must be the change you wish to see in the world. -- Gandhi
Be Free! --   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer

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