From: Ondřej Surý <ondrej@isc.org>
Date: Thu, 11 Apr 2024 01:16:12 +0000 (+0200)
Subject: Use atomic operations to access the trust byte in ncache data
X-Git-Tag: v9.19.24~31^2~1
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=eb1829b9708d6dd42f2a96f08cf69b18a3bee31c;p=thirdparty%2Fbind9.git

Use atomic operations to access the trust byte in ncache data

Protect the access to the trust byte in the ncache data with relaxed
atomic operation to mimick the current behaviour.  This will teach
TSAN that the concurrent access is fine.
---

diff --git a/lib/dns/ncache.c b/lib/dns/ncache.c
index f6ec3cbb93f..43e29c80e4d 100644
--- a/lib/dns/ncache.c
+++ b/lib/dns/ncache.c
@@ -42,6 +42,14 @@
  *
  */
 
+static uint8_t
+atomic_getuint8(isc_buffer_t *b) {
+	atomic_uchar *cp = isc_buffer_current(b);
+	uint8_t ret = atomic_load_relaxed(cp);
+	isc_buffer_forward(b, 1);
+	return (ret);
+}
+
 static isc_result_t
 addoptout(dns_message_t *message, dns_db_t *cache, dns_dbnode_t *node,
 	  dns_rdatatype_t covers, isc_stdtime_t now, dns_ttl_t minttl,
@@ -493,10 +501,10 @@ rdataset_count(dns_rdataset_t *rdataset) {
 
 static void
 rdataset_settrust(dns_rdataset_t *rdataset, dns_trust_t trust) {
-	unsigned char *raw;
+	atomic_uchar *raw;
 
-	raw = rdataset->ncache.raw;
-	raw[-1] = (unsigned char)trust;
+	raw = (atomic_uchar *)rdataset->ncache.raw;
+	atomic_store_relaxed(&raw[-1], (unsigned char)trust);
 	rdataset->trust = trust;
 }
 
@@ -548,7 +556,7 @@ dns_ncache_getrdataset(dns_rdataset_t *ncacherdataset, dns_name_t *name,
 		ttype = isc_buffer_getuint16(&source);
 
 		if (ttype == type && dns_name_equal(&tname, name)) {
-			trust = isc_buffer_getuint8(&source);
+			trust = atomic_getuint8(&source);
 			INSIST(trust <= dns_trust_ultimate);
 			isc_buffer_remainingregion(&source, &remaining);
 			break;
@@ -627,7 +635,7 @@ dns_ncache_getsigrdataset(dns_rdataset_t *ncacherdataset, dns_name_t *name,
 		}
 
 		INSIST(remaining.length >= 1);
-		trust = isc_buffer_getuint8(&source);
+		trust = atomic_getuint8(&source);
 		INSIST(trust <= dns_trust_ultimate);
 		isc_region_consume(&remaining, 1);
 
@@ -705,7 +713,7 @@ dns_ncache_current(dns_rdataset_t *ncacherdataset, dns_name_t *found,
 
 	INSIST(remaining.length >= 5);
 	type = isc_buffer_getuint16(&source);
-	trust = isc_buffer_getuint8(&source);
+	trust = atomic_getuint8(&source);
 	INSIST(trust <= dns_trust_ultimate);
 	isc_buffer_remainingregion(&source, &remaining);