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From dc512364e8490facb30f8c23fcc496d21adfc4e4 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Wed, 24 Jul 2024 12:06:47 +0200
Subject: [PATCH 05/12] resolv: Allow short error responses to match any query
(bug 31890)
Reviewed-by: DJ Delorie <dj@redhat.com>
(cherry picked from commit 691a3b2e9bfaba842e46a5ccb7f5e6ea144c3ade)
---
NEWS | 1 +
resolv/Makefile | 3 +
resolv/res_send.c | 29 +++++---
resolv/tst-resolv-short-response.c | 112 +++++++++++++++++++++++++++++
4 files changed, 135 insertions(+), 10 deletions(-)
create mode 100644 resolv/tst-resolv-short-response.c
diff --git a/NEWS b/NEWS
index f0a0834496..c331604747 100644
--- a/NEWS
+++ b/NEWS
@@ -51,6 +51,7 @@ The following bugs are resolved with this release:
[31183] Wide stream buffer size reduced MB_LEN_MAX bytes after bug 17522 fix
[31184] FAIL: elf/tst-tlsgap
[31185] Incorrect thread point access in _dl_tlsdesc_undefweak and _dl_tlsdesc_dynamic
+ [31890] resolv: Allow short error responses to match any DNS query
[31965] rseq extension mechanism does not work as intended
diff --git a/resolv/Makefile b/resolv/Makefile
index 2f99eb3862..cca0748f9a 100644
--- a/resolv/Makefile
+++ b/resolv/Makefile
@@ -106,6 +106,7 @@ tests += \
tst-resolv-nondecimal \
tst-resolv-res_init-multi \
tst-resolv-search \
+ tst-resolv-short-response \
tst-resolv-trailing \
# This test calls __res_context_send directly, which is not exported
@@ -299,6 +300,8 @@ $(objpfx)tst-resolv-nondecimal: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-qtypes: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-rotate: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-search: $(objpfx)libresolv.so $(shared-thread-library)
+$(objpfx)tst-resolv-short-response: $(objpfx)libresolv.so \
+ $(shared-thread-library)
$(objpfx)tst-resolv-trailing: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-threads: $(objpfx)libresolv.so $(shared-thread-library)
$(objpfx)tst-resolv-txnid-collision: $(objpfx)libresolv.a \
diff --git a/resolv/res_send.c b/resolv/res_send.c
index d098eba470..bf4ce67b1d 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -1197,19 +1197,30 @@ send_dg(res_state statp,
}
/* Check for the correct header layout and a matching
- question. */
+ question. Some recursive resolvers send REFUSED
+ without copying back the question section
+ (producing a response that is only HFIXEDSZ bytes
+ long). Skip query matching in this case. */
+ bool thisansp_error = (anhp->rcode == SERVFAIL ||
+ anhp->rcode == NOTIMP ||
+ anhp->rcode == REFUSED);
+ bool skip_query_match = (*thisresplenp == HFIXEDSZ
+ && ntohs (anhp->qdcount) == 0
+ && thisansp_error);
int matching_query = 0; /* Default to no matching query. */
if (!recvresp1
&& anhp->id == hp->id
- && __libc_res_queriesmatch (buf, buf + buflen,
- *thisansp,
- *thisansp + *thisanssizp))
+ && (skip_query_match
+ || __libc_res_queriesmatch (buf, buf + buflen,
+ *thisansp,
+ *thisansp + *thisanssizp)))
matching_query = 1;
if (!recvresp2
&& anhp->id == hp2->id
- && __libc_res_queriesmatch (buf2, buf2 + buflen2,
- *thisansp,
- *thisansp + *thisanssizp))
+ && (skip_query_match
+ || __libc_res_queriesmatch (buf2, buf2 + buflen2,
+ *thisansp,
+ *thisansp + *thisanssizp)))
matching_query = 2;
if (matching_query == 0)
/* Spurious UDP packet. Drop it and continue
@@ -1219,9 +1230,7 @@ send_dg(res_state statp,
goto wait;
}
- if (anhp->rcode == SERVFAIL ||
- anhp->rcode == NOTIMP ||
- anhp->rcode == REFUSED) {
+ if (thisansp_error) {
next_ns:
if (recvresp1 || (buf2 != NULL && recvresp2)) {
*resplen2 = 0;
diff --git a/resolv/tst-resolv-short-response.c b/resolv/tst-resolv-short-response.c
new file mode 100644
index 0000000000..cf1e39876f
--- /dev/null
+++ b/resolv/tst-resolv-short-response.c
@@ -0,0 +1,112 @@
+/* Test for spurious timeouts with short 12-byte responses (bug 31890).
+ Copyright (C) 2024 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <resolv.h>
+#include <support/check.h>
+#include <support/resolv_test.h>
+#include <support/check_nss.h>
+
+/* The rcode in the initial response. */
+static volatile int rcode;
+
+static void
+response (const struct resolv_response_context *ctx,
+ struct resolv_response_builder *b,
+ const char *qname, uint16_t qclass, uint16_t qtype)
+{
+ switch (ctx->server_index)
+ {
+ case 0:
+ /* First server times out. */
+ struct resolv_response_flags flags = {.rcode = rcode};
+ resolv_response_init (b, flags);
+ break;
+ case 1:
+ /* Second server sends reply. */
+ 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);
+ switch (qtype)
+ {
+ case T_A:
+ {
+ char ipv4[4] = {192, 0, 2, 17};
+ resolv_response_add_data (b, &ipv4, sizeof (ipv4));
+ }
+ break;
+ case T_AAAA:
+ {
+ char ipv6[16]
+ = {0x20, 0x01, 0xd, 0xb8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1};
+ resolv_response_add_data (b, &ipv6, sizeof (ipv6));
+ }
+ break;
+ default:
+ FAIL_EXIT1 ("unexpected TYPE%d query", qtype);
+ }
+ resolv_response_close_record (b);
+ break;
+ default:
+ FAIL_EXIT1 ("unexpected query to server %d", ctx->server_index);
+ }
+}
+
+static void
+check_one (void)
+{
+
+ /* The buggy 1-second query timeout results in 30 seconds of delay,
+ which triggers a test timeout failure. */
+ for (int i = 0; i < 10; ++i)
+ {
+ check_hostent ("www.example", gethostbyname ("www.example"),
+ "name: www.example\n"
+ "address: 192.0.2.17\n");
+ check_hostent ("www.example", gethostbyname2 ("www.example", AF_INET6),
+ "name: www.example\n"
+ "address: 2001:db8::1\n");
+ }
+}
+
+static int
+do_test (void)
+{
+ struct resolv_test *aux = resolv_test_start
+ ((struct resolv_redirect_config)
+ {
+ .response_callback = response,
+ });
+
+ _res.options |= RES_SNGLKUP;
+
+ rcode = 2; /* SERVFAIL. */
+ check_one ();
+
+ rcode = 4; /* NOTIMP. */
+ check_one ();
+
+ rcode = 5; /* REFUSED. */
+ check_one ();
+
+ resolv_test_end (aux);
+
+ return 0;
+}
+
+#include <support/test-driver.c>
--
2.33.0
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