commit 44500cbb25bc6e76723304b9ff39f875c04309f9
Author: Florian Weimer <fweimer@redhat.com>
Date: Thu Apr 13 13:22:51 2017 +0200
resolv: Remove EDNS fallback [BZ #21369]
EDNS is disabled by default (so there is interoperability issue), and
the fallback code is problematic because it prevents an application
from obtaining DNSSEC data after a FORMERR response.
diff --git a/resolv/res_query.c b/resolv/res_query.c
index c3ebcbf6b50fcf4b..ec65bab04153c2ff 100644
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -122,7 +122,6 @@ __libc_res_nquery(res_state statp,
HEADER *hp = (HEADER *) answer;
HEADER *hp2;
int n, use_malloc = 0;
- u_int oflags = statp->_flags;
size_t bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * QUERYSIZE;
u_char *buf = alloca (bufsize);
@@ -145,8 +144,7 @@ __libc_res_nquery(res_state statp,
query1, bufsize);
if (n > 0)
{
- if ((oflags & RES_F_EDNS0ERR) == 0
- && (statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
+ if ((statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
{
/* Use RESOLV_EDNS_BUFFER_SIZE because the receive
buffer can be reallocated. */
@@ -170,7 +168,6 @@ __libc_res_nquery(res_state statp,
n = res_nmkquery(statp, QUERY, name, class, T_AAAA, NULL, 0,
NULL, query2, bufsize - nused);
if (n > 0
- && (oflags & RES_F_EDNS0ERR) == 0
&& (statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
/* Use RESOLV_EDNS_BUFFER_SIZE because the receive
buffer can be reallocated. */
@@ -187,7 +184,6 @@ __libc_res_nquery(res_state statp,
query1, bufsize);
if (n > 0
- && (oflags & RES_F_EDNS0ERR) == 0
&& (statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
{
/* Use RESOLV_EDNS_BUFFER_SIZE if the receive buffer
@@ -215,16 +211,6 @@ __libc_res_nquery(res_state statp,
}
}
if (__glibc_unlikely (n <= 0)) {
- /* If the query choked with EDNS0, retry without EDNS0. */
- if ((statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0
- && ((oflags ^ statp->_flags) & RES_F_EDNS0ERR) != 0) {
- statp->_flags |= RES_F_EDNS0ERR;
-#ifdef DEBUG
- if (statp->options & RES_DEBUG)
- printf(";; res_nquery: retry without EDNS0\n");
-#endif
- goto again;
- }
#ifdef DEBUG
if (statp->options & RES_DEBUG)
printf(";; res_query: mkquery failed\n");
diff --git a/resolv/res_send.c b/resolv/res_send.c
index 77d59dcc4e3b8d23..98968d6239d0c8f7 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -1321,26 +1321,6 @@ send_dg(res_state statp,
? *thisanssizp : *thisresplenp);
goto wait;
}
-#ifdef RES_USE_EDNS0
- if (anhp->rcode == FORMERR
- && (statp->options & RES_USE_EDNS0) != 0U) {
- /*
- * Do not retry if the server does not understand
- * EDNS0. The case has to be captured here, as
- * FORMERR packet do not carry query section, hence
- * res_queriesmatch() returns 0.
- */
- DprintQ(statp->options & RES_DEBUG,
- (stdout,
- "server rejected query with EDNS0:\n"),
- *thisansp,
- (*thisresplenp > *thisanssizp)
- ? *thisanssizp : *thisresplenp);
- /* record the error */
- statp->_flags |= RES_F_EDNS0ERR;
- return close_and_return_error (statp, resplen2);
- }
-#endif
if (!(statp->options & RES_INSECURE2)
&& (recvresp1 || !res_queriesmatch(buf, buf + buflen,
*thisansp,
diff --git a/resolv/tst-resolv-edns.c b/resolv/tst-resolv-edns.c
index f17dbc3450f52b85..093a4f5f22aaaa51 100644
--- a/resolv/tst-resolv-edns.c
+++ b/resolv/tst-resolv-edns.c
@@ -115,8 +115,23 @@ response (const struct resolv_response_context *ctx,
{
TEST_VERIFY_EXIT (qname != NULL);
- /* The "tcp." prefix can be used to request TCP fallback. */
const char *qname_compare = qname;
+
+ /* The "formerr." prefix can be used to request a FORMERR response on the
+ first server. */
+ bool send_formerr;
+ if (strncmp ("formerr.", qname, strlen ("formerr.")) == 0)
+ {
+ send_formerr = true;
+ qname_compare = qname + strlen ("formerr.");
+ }
+ else
+ {
+ send_formerr = false;
+ qname_compare = qname;
+ }
+
+ /* The "tcp." prefix can be used to request TCP fallback. */
bool force_tcp;
if (strncmp ("tcp.", qname_compare, strlen ("tcp.")) == 0)
{
@@ -132,14 +147,20 @@ response (const struct resolv_response_context *ctx,
else
{
support_record_failure ();
- printf ("error: unexpected QNAME: %s\n", qname);
+ printf ("error: unexpected QNAME: %s (reduced: %s)\n",
+ qname, qname_compare);
return;
}
TEST_VERIFY_EXIT (qclass == C_IN);
- struct resolv_response_flags flags = {.tc = force_tcp && !ctx->tcp};
+ struct resolv_response_flags flags = { };
+ flags.tc = force_tcp && !ctx->tcp;
+ if (!flags.tc && send_formerr && ctx->server_index == 0)
+ /* Send a FORMERR for the first full response from the first
+ server. */
+ flags.rcode = 1; /* FORMERR */
resolv_response_init (b, flags);
resolv_response_add_question (b, qname, qclass, qtype);
- if (flags.tc)
+ if (flags.tc || flags.rcode != 0)
return;
if (test_verbose)
@@ -466,33 +487,42 @@ do_test (void)
for (int do_edns = 0; do_edns < 2; ++do_edns)
for (int do_dnssec = 0; do_dnssec < 2; ++do_dnssec)
for (int do_tcp = 0; do_tcp < 2; ++do_tcp)
- {
- struct resolv_test *aux = resolv_test_start
- ((struct resolv_redirect_config)
- {
- .response_callback = response,
- });
-
- use_edns = do_edns;
- if (do_edns)
- _res.options |= RES_USE_EDNS0;
- use_dnssec = do_dnssec;
- if (do_dnssec)
- _res.options |= RES_USE_DNSSEC;
-
- char *probe_name = xstrdup (EDNS_PROBE_EXAMPLE);
- if (do_tcp)
- {
- char *n = xasprintf ("tcp.%s", probe_name);
- free (probe_name);
- probe_name = n;
- }
+ for (int do_formerr = 0; do_formerr < 2; ++do_formerr)
+ {
+ struct resolv_test *aux = resolv_test_start
+ ((struct resolv_redirect_config)
+ {
+ .response_callback = response,
+ });
+
+ use_edns = do_edns;
+ if (do_edns)
+ _res.options |= RES_USE_EDNS0;
+ use_dnssec = do_dnssec;
+ if (do_dnssec)
+ _res.options |= RES_USE_DNSSEC;
+
+ char *probe_name = xstrdup (EDNS_PROBE_EXAMPLE);
+ if (do_tcp)
+ {
+ char *n = xasprintf ("tcp.%s", probe_name);
+ free (probe_name);
+ probe_name = n;
+ }
+ if (do_formerr)
+ {
+ /* Send a garbage query in an attempt to trigger EDNS
+ fallback. */
+ char *n = xasprintf ("formerr.%s", probe_name);
+ gethostbyname (n);
+ free (n);
+ }
- run_test (probe_name);
+ run_test (probe_name);
- free (probe_name);
- resolv_test_end (aux);
- }
+ free (probe_name);
+ resolv_test_end (aux);
+ }
free_response_data ();
return 0;