commit 765325951ac5c7d072278c9424930b29657e9758
Author: Florian Weimer <fweimer@redhat.com>
Date: Wed Jul 24 12:06:47 2024 +0200
resolv: Implement strict-error stub resolver option (bug 27929)
For now, do not enable this mode by default due to the potential
impact on compatibility with existing deployments.
Reviewed-by: DJ Delorie <dj@redhat.com>
diff --git a/resolv/res_init.c b/resolv/res_init.c
index 243532b3ade338d8..b838dc70642e1935 100644
--- a/resolv/res_init.c
+++ b/resolv/res_init.c
@@ -695,6 +695,7 @@ res_setoptions (struct resolv_conf_parser *parser, const char *options)
{ STRnLEN ("use-vc"), RES_USEVC },
{ STRnLEN ("trust-ad"), RES_TRUSTAD },
{ STRnLEN ("no-aaaa"), RES_NOAAAA },
+ { STRnLEN ("strict-error"), RES_STRICTERR },
};
#define noptions (sizeof (options) / sizeof (options[0]))
bool negate_option = *cp == '-';
diff --git a/resolv/res_send.c b/resolv/res_send.c
index 9c77613f374e5469..9a284ed44aa8cc2e 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -1234,21 +1234,38 @@ send_dg(res_state statp,
if (thisansp_error) {
next_ns:
- if (recvresp1 || (buf2 != NULL && recvresp2)) {
- *resplen2 = 0;
- return resplen;
- }
- if (buf2 != NULL && !single_request)
+ /* Outside of strict-error mode, use the first
+ response even if the second response is an
+ error. This allows parallel resolution to
+ succeed even if the recursive resolver
+ always answers with SERVFAIL for AAAA
+ queries (which still happens in practice
+ unfortunately).
+
+ In strict-error mode, always switch to the
+ next server and try to get a response from
+ there. */
+ if ((statp->options & RES_STRICTERR) == 0)
{
- /* No data from the first reply. */
- resplen = 0;
- /* We are waiting for a possible second reply. */
- if (matching_query == 1)
- recvresp1 = 1;
- else
- recvresp2 = 1;
-
- goto wait;
+ if (recvresp1 || (buf2 != NULL && recvresp2))
+ {
+ *resplen2 = 0;
+ return resplen;
+ }
+
+ if (buf2 != NULL && !single_request)
+ {
+ /* No data from the first reply. */
+ resplen = 0;
+ /* We are waiting for a possible
+ second reply. */
+ if (matching_query == 1)
+ recvresp1 = 1;
+ else
+ recvresp2 = 1;
+
+ goto wait;
+ }
}
/* don't retry if called from dig */
diff --git a/resolv/resolv.h b/resolv/resolv.h
index f40d6c58cee0f585..b8a0f66a5fd50e22 100644
--- a/resolv/resolv.h
+++ b/resolv/resolv.h
@@ -133,6 +133,7 @@ struct res_sym {
#define RES_NORELOAD 0x02000000 /* No automatic configuration reload. */
#define RES_TRUSTAD 0x04000000 /* Request AD bit, keep it in responses. */
#define RES_NOAAAA 0x08000000 /* Suppress AAAA queries. */
+#define RES_STRICTERR 0x10000000 /* Report more DNS errors as errors. */
#define RES_DEFAULT (RES_RECURSE|RES_DEFNAMES|RES_DNSRCH)
diff --git a/resolv/tst-resolv-res_init-skeleton.c b/resolv/tst-resolv-res_init-skeleton.c
index d3a19eb305d41467..e41bcebd9d9a8024 100644
--- a/resolv/tst-resolv-res_init-skeleton.c
+++ b/resolv/tst-resolv-res_init-skeleton.c
@@ -129,6 +129,7 @@ print_resp (FILE *fp, res_state resp)
print_option_flag (fp, &options, RES_NORELOAD, "no-reload");
print_option_flag (fp, &options, RES_TRUSTAD, "trust-ad");
print_option_flag (fp, &options, RES_NOAAAA, "no-aaaa");
+ print_option_flag (fp, &options, RES_STRICTERR, "strict-error");
fputc ('\n', fp);
if (options != 0)
fprintf (fp, "; error: unresolved option bits: 0x%x\n", options);
@@ -741,6 +742,15 @@ struct test_case test_cases[] =
"nameserver 192.0.2.1\n"
"; nameserver[0]: [192.0.2.1]:53\n"
},
+ {.name = "strict-error flag",
+ .conf = "options strict-error\n"
+ "nameserver 192.0.2.1\n",
+ .expected = "options strict-error\n"
+ "search example.com\n"
+ "; search[0]: example.com\n"
+ "nameserver 192.0.2.1\n"
+ "; nameserver[0]: [192.0.2.1]:53\n"
+ },
{ NULL }
};
diff --git a/resolv/tst-resolv-semi-failure.c b/resolv/tst-resolv-semi-failure.c
index aa9798b5a7dfaa88..b7681210f450bb5a 100644
--- a/resolv/tst-resolv-semi-failure.c
+++ b/resolv/tst-resolv-semi-failure.c
@@ -67,6 +67,9 @@ response (const struct resolv_response_context *ctx,
resolv_response_close_record (b);
}
+/* Set to 1 if strict error checking is enabled. */
+static int do_strict_error;
+
static void
check_one (void)
{
@@ -83,7 +86,10 @@ check_one (void)
struct addrinfo *ai;
int ret = getaddrinfo ("www.example", "80", &hints, &ai);
const char *expected;
- if (ret == 0 && ai->ai_next != NULL)
+ /* In strict-error mode, a switch to the second name server
+ happens, and both responses are received, so a single
+ response is a bug. */
+ if (do_strict_error || (ret == 0 && ai->ai_next != NULL))
expected = ("address: STREAM/TCP 192.0.2.17 80\n"
"address: STREAM/TCP 2001:db8::1 80\n");
else
@@ -99,33 +105,36 @@ check_one (void)
static int
do_test (void)
{
- for (int do_single_lookup = 0; do_single_lookup < 2; ++do_single_lookup)
- {
- struct resolv_test *aux = resolv_test_start
- ((struct resolv_redirect_config)
- {
- .response_callback = response,
- });
+ for (do_strict_error = 0; do_strict_error < 2; ++do_strict_error)
+ for (int do_single_lookup = 0; do_single_lookup < 2; ++do_single_lookup)
+ {
+ struct resolv_test *aux = resolv_test_start
+ ((struct resolv_redirect_config)
+ {
+ .response_callback = response,
+ });
- if (do_single_lookup)
- _res.options |= RES_SNGLKUP;
+ if (do_strict_error)
+ _res.options |= RES_STRICTERR;
+ if (do_single_lookup)
+ _res.options |= RES_SNGLKUP;
- for (int do_fail_aaaa = 0; do_fail_aaaa < 2; ++do_fail_aaaa)
- {
- fail_aaaa = do_fail_aaaa;
+ for (int do_fail_aaaa = 0; do_fail_aaaa < 2; ++do_fail_aaaa)
+ {
+ fail_aaaa = do_fail_aaaa;
- rcode = 2; /* SERVFAIL. */
- check_one ();
+ rcode = 2; /* SERVFAIL. */
+ check_one ();
- rcode = 4; /* NOTIMP. */
- check_one ();
+ rcode = 4; /* NOTIMP. */
+ check_one ();
- rcode = 5; /* REFUSED. */
- check_one ();
- }
+ rcode = 5; /* REFUSED. */
+ check_one ();
+ }
- resolv_test_end (aux);
- }
+ resolv_test_end (aux);
+ }
return 0;
}