Commit 541b675336 for bind
commit 541b675336a919fdab9cdf04f97d387f2252d959
Author: Ondřej Surý <ondrej@isc.org>
Date: Tue Sep 29 07:57:02 2026 +0200
Accept compressed names in the types RFC 3597 lists
RFC 3597 section 4 asks receivers to decompress names in RP, AFSDB, RT,
SIG, PX, NXT, NAPTR and SRV, because older senders compressed them and
some still do, yet their fromwire handlers forbade it. Unfortunately,
even though RFC 2782 is 26 years old, Microsoft servers still compress
SRV records, so we can't drop the decompression support for SRV records.
diff --git a/doc/dev/rdata.md b/doc/dev/rdata.md
index a097a91e39..18c5ec4704 100644
--- a/doc/dev/rdata.md
+++ b/doc/dev/rdata.md
@@ -213,6 +213,11 @@ name compression is allowed, according to RFC 3597.
dctx = dns_decompress_setpermitted(dctx, true); /* or false */
+It is allowed for the types defined in RFC 1035, and for the older
+types that RFC 3597 section 4 asks receivers to decompress (RP, AFSDB,
+RT, SIG, PX, NXT, NAPTR and SRV) even though their `towire_typename()`
+must not compress them.
+
|Parameter|Description |
|---------|-----------------------|
|`class`|This argument should be ignored when used with a class-generic RR type otherwise `REQUIRE(class == <value>)` should be present at the start of the function.|
diff --git a/lib/dns/rdata/generic/afsdb_18.c b/lib/dns/rdata/generic/afsdb_18.c
index edbaa7b384..bdd54d5d37 100644
--- a/lib/dns/rdata/generic/afsdb_18.c
+++ b/lib/dns/rdata/generic/afsdb_18.c
@@ -102,7 +102,11 @@ fromwire_afsdb(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
dns_name_init(&name);
diff --git a/lib/dns/rdata/generic/naptr_35.c b/lib/dns/rdata/generic/naptr_35.c
index 158dea6f88..5acdcbd0f7 100644
--- a/lib/dns/rdata/generic/naptr_35.c
+++ b/lib/dns/rdata/generic/naptr_35.c
@@ -310,7 +310,11 @@ fromwire_naptr(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
dns_name_init(&name);
diff --git a/lib/dns/rdata/generic/nxt_30.c b/lib/dns/rdata/generic/nxt_30.c
index 1eec28ffd8..7862e25c37 100644
--- a/lib/dns/rdata/generic/nxt_30.c
+++ b/lib/dns/rdata/generic/nxt_30.c
@@ -142,7 +142,11 @@ fromwire_nxt(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
dns_name_init(&name);
RETERR(dns_name_fromwire(&name, source, dctx, target));
diff --git a/lib/dns/rdata/generic/rp_17.c b/lib/dns/rdata/generic/rp_17.c
index ee1b683895..4d3cedf2a3 100644
--- a/lib/dns/rdata/generic/rp_17.c
+++ b/lib/dns/rdata/generic/rp_17.c
@@ -106,7 +106,11 @@ fromwire_rp(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
dns_name_init(&rmail);
dns_name_init(&email);
diff --git a/lib/dns/rdata/generic/rt_21.c b/lib/dns/rdata/generic/rt_21.c
index 8323f9233c..ca1806e313 100644
--- a/lib/dns/rdata/generic/rt_21.c
+++ b/lib/dns/rdata/generic/rt_21.c
@@ -101,7 +101,11 @@ fromwire_rt(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
dns_name_init(&name);
diff --git a/lib/dns/rdata/generic/sig_24.c b/lib/dns/rdata/generic/sig_24.c
index 4328659412..35cede14d8 100644
--- a/lib/dns/rdata/generic/sig_24.c
+++ b/lib/dns/rdata/generic/sig_24.c
@@ -265,7 +265,11 @@ fromwire_sig(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
isc_buffer_activeregion(source, &sr);
/*
diff --git a/lib/dns/rdata/in_1/px_26.c b/lib/dns/rdata/in_1/px_26.c
index cfc24d5d3c..1cd16839f8 100644
--- a/lib/dns/rdata/in_1/px_26.c
+++ b/lib/dns/rdata/in_1/px_26.c
@@ -118,7 +118,11 @@ fromwire_in_px(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
dns_name_init(&name);
diff --git a/lib/dns/rdata/in_1/srv_33.c b/lib/dns/rdata/in_1/srv_33.c
index 73de807268..a61360c4f3 100644
--- a/lib/dns/rdata/in_1/srv_33.c
+++ b/lib/dns/rdata/in_1/srv_33.c
@@ -153,7 +153,11 @@ fromwire_in_srv(ARGS_FROMWIRE) {
UNUSED(type);
UNUSED(rdclass);
- dctx = dns_decompress_setpermitted(dctx, false);
+ /*
+ * RFC 3597 section 4 asks receivers to decompress this type,
+ * even though senders must not compress it.
+ */
+ dctx = dns_decompress_setpermitted(dctx, true);
dns_name_init(&name);
diff --git a/tests/dns/rdata_test.c b/tests/dns/rdata_test.c
index a16bbab77a..40f84f3810 100644
--- a/tests/dns/rdata_test.c
+++ b/tests/dns/rdata_test.c
@@ -3689,6 +3689,115 @@ ISC_RUN_TEST_IMPL(zonemd) {
dns_rdatatype_zonemd, sizeof(dns_rdata_zonemd_t));
}
+/*
+ * Compression pointers are only permitted in the rdata of the types
+ * defined in RFC 1035, and of the older types that RFC 3597 section 4
+ * asks receivers to decompress: RP, AFSDB, RT, SIG, PX, NXT, NAPTR and
+ * SRV. Each type's fromwire handler sets the policy for its own rdata,
+ * so unless the caller passes DNS_DECOMPRESS_ALWAYS, a pointer in any
+ * other type is rejected with DNS_R_DISALLOWED. Exercise this for MX,
+ * for each of the RFC 3597 types, and for a disallowed type (DNAME),
+ * with a context that arrives with compression permitted, to show that
+ * the policy is set per type rather than inherited from the caller.
+ *
+ * Each wire buffer starts with the name "example.com." at offset 0
+ * so every 0xc0 0x00 compression pointer in the rdata refers back to
+ * a syntactically valid name. Parsing of the rdata starts at the
+ * OWNER_LEN offset.
+ */
+ISC_RUN_TEST_IMPL(decompression_permitted) {
+#define OWNER 0x07, 'e', 'x', 'a', 'm', 'p', 'l', 'e', 0x03, 'c', 'o', 'm', 0x00
+ static const size_t OWNER_LEN = 13;
+ static const unsigned char mx_wire[] = {
+ OWNER, 0x00, 0x0a, /* preference */
+ 0xc0, 0x00, /* exchange: pointer */
+ };
+ static const unsigned char rp_wire[] = {
+ OWNER, 0xc0, 0x00, /* mbox: pointer */
+ 0xc0, 0x00, /* txt: pointer */
+ };
+ static const unsigned char afsdb_wire[] = {
+ OWNER, 0x00, 0x01, /* subtype */
+ 0xc0, 0x00, /* hostname: pointer */
+ };
+ static const unsigned char rt_wire[] = {
+ OWNER, 0x00, 0x0a, /* preference */
+ 0xc0, 0x00, /* intermediate host: pointer */
+ };
+ static const unsigned char sig_wire[] = {
+ OWNER, 0x00, 0x01, 0x08, 0x02, /* covered/algorithm/labels */
+ 0x00, 0x00, 0x0e, 0x10, /* original TTL */
+ 0x00, 0x00, 0x00, 0x00, /* expiration */
+ 0x00, 0x00, 0x00, 0x00, /* inception */
+ 0x00, 0x01, /* key tag */
+ 0xc0, 0x00, /* signer: pointer */
+ 0x01, /* signature */
+ };
+ static const unsigned char px_wire[] = {
+ OWNER, 0x00, 0x0a, /* preference */
+ 0xc0, 0x00, /* MAP822: pointer */
+ 0xc0, 0x00, /* MAPX400: pointer */
+ };
+ /* next domain: pointer */
+ static const unsigned char nxt_wire[] = { OWNER, 0xc0, 0x00 };
+ static const unsigned char naptr_wire[] = {
+ OWNER, 0x00, 0x0a, 0x00, 0x14, /* order/preference */
+ 0x00, 0x00, 0x00, /* flags/service/regexp */
+ 0xc0, 0x00, /* replacement: pointer */
+ };
+ static const unsigned char srv_wire[] = {
+ OWNER, 0x00, 0x0a, 0x00,
+ 0x14, 0x00, 0x50, /* priority/weight/port */
+ 0xc0, 0x00, /* target: pointer */
+ };
+ /* target: pointer */
+ static const unsigned char dname_wire[] = { OWNER, 0xc0, 0x00 };
+#undef OWNER
+
+ const struct {
+ const unsigned char *wire;
+ size_t wire_len;
+ dns_rdatatype_t type;
+ isc_result_t expected;
+ } cases[] = {
+ { mx_wire, sizeof(mx_wire), dns_rdatatype_mx, ISC_R_SUCCESS },
+ { rp_wire, sizeof(rp_wire), dns_rdatatype_rp, ISC_R_SUCCESS },
+ { afsdb_wire, sizeof(afsdb_wire), dns_rdatatype_afsdb,
+ ISC_R_SUCCESS },
+ { rt_wire, sizeof(rt_wire), dns_rdatatype_rt, ISC_R_SUCCESS },
+ { sig_wire, sizeof(sig_wire), dns_rdatatype_sig,
+ ISC_R_SUCCESS },
+ { px_wire, sizeof(px_wire), dns_rdatatype_px, ISC_R_SUCCESS },
+ { nxt_wire, sizeof(nxt_wire), dns_rdatatype_nxt,
+ ISC_R_SUCCESS },
+ { naptr_wire, sizeof(naptr_wire), dns_rdatatype_naptr,
+ ISC_R_SUCCESS },
+ { srv_wire, sizeof(srv_wire), dns_rdatatype_srv,
+ ISC_R_SUCCESS },
+ { dname_wire, sizeof(dname_wire), dns_rdatatype_dname,
+ DNS_R_DISALLOWED },
+ };
+
+ for (size_t i = 0; i < ARRAY_SIZE(cases); i++) {
+ isc_buffer_t source, target;
+ unsigned char buf[256];
+ dns_rdata_t rdata = DNS_RDATA_INIT;
+ isc_result_t result;
+
+ isc_buffer_constinit(&source, cases[i].wire, cases[i].wire_len);
+ isc_buffer_add(&source, cases[i].wire_len);
+ isc_buffer_forward(&source, OWNER_LEN);
+ isc_buffer_setactive(&source, cases[i].wire_len - OWNER_LEN);
+
+ isc_buffer_init(&target, buf, sizeof(buf));
+
+ result = dns_rdata_fromwire(&rdata, dns_rdataclass_in,
+ cases[i].type, &source,
+ DNS_DECOMPRESS_PERMITTED, &target);
+ assert_int_equal(result, cases[i].expected);
+ }
+}
+
ISC_RUN_TEST_IMPL(atcname) {
unsigned int i;
@@ -3854,6 +3963,7 @@ ISC_TEST_ENTRY(zonemd)
/* other tests */
ISC_TEST_ENTRY(edns_client_subnet)
ISC_TEST_ENTRY(edns_rad)
+ISC_TEST_ENTRY(decompression_permitted)
ISC_TEST_ENTRY(atcname)
ISC_TEST_ENTRY(atparent)
ISC_TEST_ENTRY(iszonecutauth)