[PATCH COMMITTED] CVE-2015-5180: resolv: Fix crash with internal QTYPE [BZ #18784]

[fweimer at redhat dot com (Florian Weimer)]

Also rename T_UNSPEC because an upcoming public header file
update will use that name.

2016-12-31  Florian Weimer  <fweimer@redhat.com>

	[BZ #18784]
	CVE-2015-5180
	* include/arpa/nameser_compat.h (T_QUERY_A_AND_AAAA): Rename from
	T_UNSPEC.  Adjust value.
	* resolv/nss_dns/dns-host.c (_nss_dns_gethostbyname4_r): Use it.
	* resolv/res_query.c (__libc_res_nquery): Likewise.
	* resolv/res_mkquery.c (res_nmkquery): Check for out-of-range
	QTYPEs.
	* resolv/tst-resolv-qtypes.c: New file.
	* resolv/Makefile (xtests): Add tst-resolv-qtypes.
	(tst-resolv-qtypes): Link against libresolv and libpthread.

diff --git a/NEWS b/NEWS
index 7ebce44..08b566d 100644
--- a/NEWS
+++ b/NEWS
@@ -191,12 +191,18 @@ Version 2.25
 
 Security related changes:
 
-  On ARM EABI (32-bit), generating a backtrace for execution contexts which
+* On ARM EABI (32-bit), generating a backtrace for execution contexts which
   have been created with makecontext could fail to terminate due to a
   missing .cantunwind annotation.  This has been observed to lead to a hang
   (denial of service) in some Go applications compiled with gccgo.  Reported
   by Andreas Schwab.  (CVE-2016-6323)
 
+* The DNS stub resolver functions would crash due to a NULL pointer
+  dereference when processing a query with a valid DNS question type which
+  was used internally in the implementation.  The stub resolver now uses a
+  question type which is outside the range of valid question type values.
+  (CVE-2015-5180)
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/include/arpa/nameser_compat.h b/include/arpa/nameser_compat.h
index 6928000..f7d0e04 100644
--- a/include/arpa/nameser_compat.h
+++ b/include/arpa/nameser_compat.h
@@ -3,9 +3,9 @@
 
 # ifndef _ISOMAC
 
-/* Picksome unused number to represent lookups of IPv4 and IPv6 (i.e.,
-   T_A and T_AAAA).  */
-#define T_UNSPEC 62321
+/* The number is outside the 16-bit RR type range and is used
+   internally by the implementation.  */
+#define T_QUERY_A_AND_AAAA 439963904
 
 # endif /* !_ISOMAC */
 #endif
diff --git a/resolv/Makefile b/resolv/Makefile
index 1e9f562..1089995 100644
--- a/resolv/Makefile
+++ b/resolv/Makefile
@@ -49,6 +49,8 @@ tests += \
   tst-resolv-network \
   tst-resolv-search \
 
+# This test sends millions of packets and is rather slow.
+xtests += tst-resolv-qtypes
 endif
 extra-libs-others = $(extra-libs)
 libresolv-routines := res_comp res_debug \
@@ -123,6 +125,7 @@ $(objpfx)tst-bug18665: $(objpfx)libresolv.so $(shared-thread-library)
 $(objpfx)tst-res_use_inet6: $(objpfx)libresolv.so $(shared-thread-library)
 $(objpfx)tst-resolv-basic: $(objpfx)libresolv.so $(shared-thread-library)
 $(objpfx)tst-resolv-network: $(objpfx)libresolv.so $(shared-thread-library)
+$(objpfx)tst-resolv-qtypes: $(objpfx)libresolv.so $(shared-thread-library)
 $(objpfx)tst-resolv-search: $(objpfx)libresolv.so $(shared-thread-library)
 
 # This test case uses the deprecated RES_USE_INET6 resolver option.
diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index 901e037..d597faa 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -324,7 +324,7 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
 
   int olderr = errno;
   enum nss_status status;
-  int n = __libc_res_nsearch (&_res, name, C_IN, T_UNSPEC,
+  int n = __libc_res_nsearch (&_res, name, C_IN, T_QUERY_A_AND_AAAA,
 			      host_buffer.buf->buf, 2048, &host_buffer.ptr,
 			      &ans2p, &nans2p, &resplen2, &ans2p_malloced);
   if (n >= 0)
diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
index 12f9730..d80b531 100644
--- a/resolv/res_mkquery.c
+++ b/resolv/res_mkquery.c
@@ -103,6 +103,10 @@ res_nmkquery(res_state statp,
 	int n;
 	u_char *dnptrs[20], **dpp, **lastdnptr;
 
+	if (class < 0 || class > 65535
+	    || type < 0 || type > 65535)
+	  return -1;
+
 #ifdef DEBUG
 	if (statp->options & RES_DEBUG)
 		printf(";; res_nmkquery(%s, %s, %s, %s)\n",
diff --git a/resolv/res_query.c b/resolv/res_query.c
index 944d1a9..07dc6f6 100644
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -122,7 +122,7 @@ __libc_res_nquery(res_state statp,
 	int n, use_malloc = 0;
 	u_int oflags = statp->_flags;
 
-	size_t bufsize = (type == T_UNSPEC ? 2 : 1) * QUERYSIZE;
+	size_t bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * QUERYSIZE;
 	u_char *buf = alloca (bufsize);
 	u_char *query1 = buf;
 	int nquery1 = -1;
@@ -137,7 +137,7 @@ __libc_res_nquery(res_state statp,
 		printf(";; res_query(%s, %d, %d)\n", name, class, type);
 #endif
 
-	if (type == T_UNSPEC)
+	if (type == T_QUERY_A_AND_AAAA)
 	  {
 	    n = res_nmkquery(statp, QUERY, name, class, T_A, NULL, 0, NULL,
 			     query1, bufsize);
@@ -190,7 +190,7 @@ __libc_res_nquery(res_state statp,
 	if (__builtin_expect (n <= 0, 0) && !use_malloc) {
 		/* Retry just in case res_nmkquery failed because of too
 		   short buffer.  Shouldn't happen.  */
-		bufsize = (type == T_UNSPEC ? 2 : 1) * MAXPACKET;
+		bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * MAXPACKET;
 		buf = malloc (bufsize);
 		if (buf != NULL) {
 			query1 = buf;
diff --git a/resolv/tst-resolv-qtypes.c b/resolv/tst-resolv-qtypes.c
new file mode 100644
index 0000000..b3e60c6
--- /dev/null
+++ b/resolv/tst-resolv-qtypes.c
@@ -0,0 +1,185 @@
+/* Exercise low-level query functions with different QTYPEs.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <resolv.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/check_nss.h>
+#include <support/resolv_test.h>
+#include <support/support.h>
+#include <support/test-driver.h>
+#include <support/xmemstream.h>
+
+/* If ture, the response function will send the actual response packet
+   over TCP instead of UDP.  */
+static volatile bool force_tcp;
+
+/* Send back a fake resource record matching the QTYPE.  */
+static void
+response (const struct resolv_response_context *ctx,
+          struct resolv_response_builder *b,
+          const char *qname, uint16_t qclass, uint16_t qtype)
+{
+  if (force_tcp && ctx->tcp)
+    {
+      resolv_response_init (b, (struct resolv_response_flags) { .tc = 1 });
+      resolv_response_add_question (b, qname, qclass, qtype);
+      return;
+    }
+
+  resolv_response_init (b, (struct resolv_response_flags) { });
+  resolv_response_add_question (b, qname, qclass, qtype);
+  resolv_response_section (b, ns_s_an);
+  resolv_response_open_record (b, qname, qclass, qtype, 0);
+  resolv_response_add_data (b, &qtype, sizeof (qtype));
+  resolv_response_close_record (b);
+}
+
+static const const char *domain = "www.example.com";
+
+static int
+wrap_res_query (int type, unsigned char *answer, int answer_length)
+{
+  return res_query (domain, C_IN, type, answer, answer_length);
+}
+
+static int
+wrap_res_search (int type, unsigned char *answer, int answer_length)
+{
+  return res_query (domain, C_IN, type, answer, answer_length);
+}
+
+static int
+wrap_res_querydomain (int type, unsigned char *answer, int answer_length)
+{
+  return res_querydomain ("www", "example.com", C_IN, type,
+                           answer, answer_length);
+}
+
+static int
+wrap_res_send (int type, unsigned char *answer, int answer_length)
+{
+  unsigned char buf[512];
+  int ret = res_mkquery (QUERY, domain, C_IN, type,
+                         (const unsigned char *) "", 0, NULL,
+                         buf, sizeof (buf));
+  if (type < 0 || type >= 65536)
+    {
+      /* res_mkquery fails for out-of-range record types.  */
+      TEST_VERIFY_EXIT (ret == -1);
+      return -1;
+    }
+  TEST_VERIFY_EXIT (ret > 12);  /* DNS header length.  */
+  return res_send (buf, ret, answer, answer_length);
+}
+
+static int
+wrap_res_nquery (int type, unsigned char *answer, int answer_length)
+{
+  return res_nquery (&_res, domain, C_IN, type, answer, answer_length);
+}
+
+static int
+wrap_res_nsearch (int type, unsigned char *answer, int answer_length)
+{
+  return res_nquery (&_res, domain, C_IN, type, answer, answer_length);
+}
+
+static int
+wrap_res_nquerydomain (int type, unsigned char *answer, int answer_length)
+{
+  return res_nquerydomain (&_res, "www", "example.com", C_IN, type,
+                           answer, answer_length);
+}
+
+static int
+wrap_res_nsend (int type, unsigned char *answer, int answer_length)
+{
+  unsigned char buf[512];
+  int ret = res_nmkquery (&_res, QUERY, domain, C_IN, type,
+                         (const unsigned char *) "", 0, NULL,
+                         buf, sizeof (buf));
+  if (type < 0 || type >= 65536)
+    {
+      /* res_mkquery fails for out-of-range record types.  */
+      TEST_VERIFY_EXIT (ret == -1);
+      return -1;
+    }
+  TEST_VERIFY_EXIT (ret > 12);  /* DNS header length.  */
+  return res_nsend (&_res, buf, ret, answer, answer_length);
+}
+
+static void
+test_function (const char *fname,
+               int (*func) (int type,
+                            unsigned char *answer, int answer_length))
+{
+  unsigned char buf[512];
+  for (int tcp = 0; tcp < 2; ++tcp)
+    {
+      force_tcp = tcp;
+      for (unsigned int type = 1; type <= 65535; ++type)
+        {
+          if (test_verbose)
+            printf ("info: sending QTYPE %d with %s (tcp=%d)\n",
+                    type, fname, tcp);
+          int ret = func (type, buf, sizeof (buf));
+          if (ret != 47)
+            FAIL_EXIT1 ("%s tcp=%d qtype=%d return value %d",
+                        fname,tcp, type, ret);
+          /* One question, one answer record.  */
+          TEST_VERIFY (memcmp (buf + 4, "\0\1\0\1\0\0\0\0", 8) == 0);
+          /* Question section.  */
+          static const char qname[] = "\3www\7example\3com";
+          size_t qname_length = sizeof (qname);
+          TEST_VERIFY (memcmp (buf + 12, qname, qname_length) == 0);
+          /* RDATA part of answer.  */
+          uint16_t type16 = type;
+          TEST_VERIFY (memcmp (buf + ret - 2, &type16, sizeof (type16)) == 0);
+        }
+    }
+
+  TEST_VERIFY (func (-1, buf, sizeof (buf) == -1));
+  TEST_VERIFY (func (65536, buf, sizeof (buf) == -1));
+}
+
+static int
+do_test (void)
+{
+  struct resolv_redirect_config config =
+    {
+      .response_callback = response,
+    };
+  struct resolv_test *obj = resolv_test_start (config);
+
+  test_function ("res_query", &wrap_res_query);
+  test_function ("res_search", &wrap_res_search);
+  test_function ("res_querydomain", &wrap_res_querydomain);
+  test_function ("res_send", &wrap_res_send);
+
+  test_function ("res_nquery", &wrap_res_nquery);
+  test_function ("res_nsearch", &wrap_res_nsearch);
+  test_function ("res_nquerydomain", &wrap_res_nquerydomain);
+  test_function ("res_nsend", &wrap_res_nsend);
+
+  resolv_test_end (obj);
+  return 0;
+}
+
+#define TIMEOUT 300
+#include <support/test-driver.c>