From: Ondřej Surý <ondrej@isc.org>
Date: Wed, 17 Dec 2025 09:01:06 +0000 (+0100)
Subject: Use offsetof() instead of pointer arithmetics to get slabheader
X-Git-Tag: v9.21.19~22^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b8e07a0b5aed51828af72af2a8d58b090088725d;p=thirdparty%2Fbind9.git

Use offsetof() instead of pointer arithmetics to get slabheader

In rdataset_getheader() a cast of the raw buffer to dns_slabheader_t and
pointer arithmetics was used to get the start of the slabheader
structure.  Use more correct offsetof(dns_slabheader_t, raw) to
calculate the correct start of the dns_slabheader_t from the flexible
member raw[].
---

diff --git a/lib/dns/rdataslab.c b/lib/dns/rdataslab.c
index c56cd3b03bc..64e955cad4e 100644
--- a/lib/dns/rdataslab.c
+++ b/lib/dns/rdataslab.c
@@ -801,8 +801,8 @@ rdataset_getownercase(const dns_rdataset_t *rdataset, dns_name_t *name) {
 
 static dns_slabheader_t *
 rdataset_getheader(const dns_rdataset_t *rdataset) {
-	dns_slabheader_t *header = (dns_slabheader_t *)rdataset->slab.raw;
-	return header - 1;
+	uint8_t *rawbuf = rdataset->slab.raw;
+	return (dns_slabheader_t *)(rawbuf - offsetof(dns_slabheader_t, raw));
 }
 
 dns_slabtop_t *