From 4601d4299a2bce82f44d997cd1c1e99bd04c9adc Mon Sep 17 00:00:00 2001
From: Evan Hunt <each@isc.org>
Date: Thu, 6 Feb 2025 15:50:52 -0800
Subject: [PATCH] fix and simplify dns_rdataset_equal() and _equalx()

if both rdataslabs being compared have zero length, return true.

also, since these functions are only ever called on slabheaders
with sizeof(dns_slabheader_t) as the reserve length, we can
simplify the API: remove the reservelen argument, and pass the
slabs as type dns_slabheader_t * instead of unsigned char *.
---
 lib/dns/include/dns/rdataslab.h |  8 +++-----
 lib/dns/qpcache.c               |  8 ++------
 lib/dns/rdataslab.c             | 20 +++++++++++---------
 3 files changed, 16 insertions(+), 20 deletions(-)

diff --git a/lib/dns/include/dns/rdataslab.h b/lib/dns/include/dns/rdataslab.h
index c81fe9777f..15437f0d4a 100644
--- a/lib/dns/include/dns/rdataslab.h
+++ b/lib/dns/include/dns/rdataslab.h
@@ -251,8 +251,7 @@ dns_rdataslab_subtract(unsigned char *mslab, unsigned char *sslab,
  */
 
 bool
-dns_rdataslab_equal(unsigned char *slab1, unsigned char *slab2,
-		    unsigned int reservelen);
+dns_rdataslab_equal(dns_slabheader_t *slab1, dns_slabheader_t *slab2);
 /*%<
  * Compare two rdataslabs for equality.  This does _not_ do a full
  * DNSSEC comparison.
@@ -264,9 +263,8 @@ dns_rdataslab_equal(unsigned char *slab1, unsigned char *slab2,
  *\li	true if the slabs are equal, false otherwise.
  */
 bool
-dns_rdataslab_equalx(unsigned char *slab1, unsigned char *slab2,
-		     unsigned int reservelen, dns_rdataclass_t rdclass,
-		     dns_rdatatype_t type);
+dns_rdataslab_equalx(dns_slabheader_t *slab1, dns_slabheader_t *slab2,
+		     dns_rdataclass_t rdclass, dns_rdatatype_t type);
 /*%<
  * Compare two rdataslabs for DNSSEC equality.
  *
diff --git a/lib/dns/qpcache.c b/lib/dns/qpcache.c
index c5ea5a1e31..f63be9ec44 100644
--- a/lib/dns/qpcache.c
+++ b/lib/dns/qpcache.c
@@ -2884,9 +2884,7 @@ find_header:
 		if (ACTIVE(header, now) && header->type == dns_rdatatype_ns &&
 		    EXISTS(header) && EXISTS(newheader) &&
 		    header->trust >= newheader->trust &&
-		    dns_rdataslab_equalx((unsigned char *)header,
-					 (unsigned char *)newheader,
-					 (unsigned int)(sizeof(*newheader)),
+		    dns_rdataslab_equalx(header, newheader,
 					 qpdb->common.rdclass,
 					 (dns_rdatatype_t)header->type))
 		{
@@ -2950,9 +2948,7 @@ find_header:
 		     header->type == DNS_SIGTYPE(dns_rdatatype_ds)) &&
 		    EXISTS(header) && EXISTS(newheader) &&
 		    header->trust >= newheader->trust &&
-		    dns_rdataslab_equal((unsigned char *)header,
-					(unsigned char *)newheader,
-					(unsigned int)(sizeof(*newheader))))
+		    dns_rdataslab_equal(header, newheader))
 		{
 			/*
 			 * Honour the new ttl if it is less than the
diff --git a/lib/dns/rdataslab.c b/lib/dns/rdataslab.c
index ce0dfeb3f4..27f85fc2f4 100644
--- a/lib/dns/rdataslab.c
+++ b/lib/dns/rdataslab.c
@@ -714,20 +714,21 @@ dns_rdataslab_subtract(unsigned char *mslab, unsigned char *sslab,
 }
 
 bool
-dns_rdataslab_equal(unsigned char *slab1, unsigned char *slab2,
-		    unsigned int reservelen) {
+dns_rdataslab_equal(dns_slabheader_t *slab1, dns_slabheader_t *slab2) {
 	unsigned char *current1 = NULL, *current2 = NULL;
 	unsigned int count1, count2;
 	unsigned int length1, length2;
 
-	current1 = slab1 + reservelen;
+	current1 = (unsigned char *)slab1 + sizeof(dns_slabheader_t);
 	count1 = get_uint16(current1);
 
-	current2 = slab2 + reservelen;
+	current2 = (unsigned char *)slab2 + sizeof(dns_slabheader_t);
 	count2 = get_uint16(current2);
 
 	if (count1 != count2) {
 		return false;
+	} else if (count1 == 0) {
+		return true;
 	}
 
 	while (count1-- > 0) {
@@ -747,22 +748,23 @@ dns_rdataslab_equal(unsigned char *slab1, unsigned char *slab2,
 }
 
 bool
-dns_rdataslab_equalx(unsigned char *slab1, unsigned char *slab2,
-		     unsigned int reservelen, dns_rdataclass_t rdclass,
-		     dns_rdatatype_t type) {
+dns_rdataslab_equalx(dns_slabheader_t *slab1, dns_slabheader_t *slab2,
+		     dns_rdataclass_t rdclass, dns_rdatatype_t type) {
 	unsigned char *current1 = NULL, *current2 = NULL;
 	unsigned int count1, count2;
 	dns_rdata_t rdata1 = DNS_RDATA_INIT;
 	dns_rdata_t rdata2 = DNS_RDATA_INIT;
 
-	current1 = slab1 + reservelen;
+	current1 = (unsigned char *)slab1 + sizeof(dns_slabheader_t);
 	count1 = get_uint16(current1);
 
-	current2 = slab2 + reservelen;
+	current2 = (unsigned char *)slab2 + sizeof(dns_slabheader_t);
 	count2 = get_uint16(current2);
 
 	if (count1 != count2) {
 		return false;
+	} else if (count1 == 0) {
+		return true;
 	}
 
 	while (count1-- > 0) {