From: Ondřej Surý <ondrej@isc.org>
Date: Thu, 23 Jun 2022 11:06:37 +0000 (+0200)
Subject: Don't compress in the rrset if compression was disabled
X-Git-Tag: v9.19.4~45^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ddad2050928e29e8175d1a79431ec15b476da727;p=thirdparty%2Fbind9.git

Don't compress in the rrset if compression was disabled

Currently, when rrset is being compressed, the optimization has been put
in place to reuse offset to the previous name in the same rrset.  This
skips the check for non-improving compression and thus compresses the
root zone making the wireformat worse by one byte.

Additionally, when the compression has been disabled for the name, it
would be repeatedly added to the compression table because we act as if
the name was not found and the dns_compress_add() doesn't check for the
existing entry.

Change the dns_name_towire2() to always lookup the name in the
compression table to prevent adding duplicates, but don't use it neither
in the wireformat nor in the rrset cache.
---

diff --git a/lib/dns/name.c b/lib/dns/name.c
index cde940e8269..0407c3b0858 100644
--- a/lib/dns/name.c
+++ b/lib/dns/name.c
@@ -1965,10 +1965,14 @@ dns_name_towire2(const dns_name_t *name, dns_compress_t *cctx,
 
 	here = target->used; /*XXX*/
 
-	if (compress) {
-		found = dns_compress_find(cctx, name, &prefix, &there);
-	} else {
+	/*
+	 * Never compress the root name.
+	 */
+	if (name->length == 1) {
 		found = false;
+		compress = false;
+	} else {
+		found = dns_compress_find(cctx, name, &prefix, &there);
 	}
 
 	/*
@@ -1976,17 +1980,17 @@ dns_name_towire2(const dns_name_t *name, dns_compress_t *cctx,
 	 * we're out of luck.
 	 */
 	if (found && there >= 0x4000) {
-		found = false;
+		compress = false;
 	}
 
 	/*
 	 * Will the compression pointer reduce the message size?
 	 */
 	if (found && (prefix.length + 2) >= name->length) {
-		found = false;
+		compress = false;
 	}
 
-	if (found) {
+	if (found && compress) {
 		if (target->length - target->used < prefix.length) {
 			return (ISC_R_NOSPACE);
 		}
@@ -2000,14 +2004,6 @@ dns_name_towire2(const dns_name_t *name, dns_compress_t *cctx,
 			return (ISC_R_NOSPACE);
 		}
 		isc_buffer_putuint16(target, there | 0xc000);
-		if (prefix.length != 0) {
-			dns_compress_add(cctx, name, &prefix, here);
-			if (comp_offsetp != NULL) {
-				*comp_offsetp = here;
-			}
-		} else if (comp_offsetp != NULL) {
-			*comp_offsetp = there;
-		}
 	} else {
 		if (target->length - target->used < name->length) {
 			return (ISC_R_NOSPACE);
@@ -2018,10 +2014,28 @@ dns_name_towire2(const dns_name_t *name, dns_compress_t *cctx,
 				      (size_t)name->length);
 		}
 		isc_buffer_add(target, name->length);
+	}
+
+	if (found && prefix.length == 0) {
+		here = there;
+	}
+
+	if (here >= 0x4000) {
+		return (ISC_R_SUCCESS);
+	}
+
+	if (found) {
+		dns_compress_add(cctx, name, &prefix, here);
+	} else {
 		dns_compress_add(cctx, name, name, here);
-		if (comp_offsetp != NULL) {
-			*comp_offsetp = here;
-		}
+	}
+
+	/*
+	 * Don't set the offset of the previously rendered name if the
+	 * compression has been disabled.
+	 */
+	if (compress && comp_offsetp != NULL) {
+		*comp_offsetp = here;
 	}
 
 	return (ISC_R_SUCCESS);