Merge pull request #49279 from nextcloud/backport/48675/stable28

[stable28] DNS: do not query CNAME if A succeeded already

Author: solracsf

lib/private/Http/Client/DnsPinMiddleware.php

@@ -74,15 +74,19 @@ private function dnsResolve(string $target, int $recursionCount) : array {
 
 		$soaDnsEntry = $this->soaRecord($target);
 		$dnsNegativeTtl = $soaDnsEntry['minimum-ttl'] ?? null;
+		$canHaveCnameRecord = true;
 
 		$dnsTypes = [DNS_A, DNS_AAAA, DNS_CNAME];
 		foreach ($dnsTypes as $dnsType) {
+			if ($canHaveCnameRecord === false && $dnsType === DNS_CNAME) {
+				continue;
+			}
+
 			if ($this->negativeDnsCache->isNegativeCached($target, $dnsType)) {
 				continue;
 			}
 
 			$dnsResponses = $this->dnsGetRecord($target, $dnsType);
-			$canHaveCnameRecord = true;
 			if ($dnsResponses !== false && count($dnsResponses) > 0) {
 				foreach ($dnsResponses as $dnsResponse) {
 					if (isset($dnsResponse['ip'])) {
@@ -93,7 +97,6 @@ private function dnsResolve(string $target, int $recursionCount) : array {
 						$canHaveCnameRecord = false;
 					} elseif (isset($dnsResponse['target']) && $canHaveCnameRecord) {
 						$targetIps = array_merge($targetIps, $this->dnsResolve($dnsResponse['target'], $recursionCount));
-						$canHaveCnameRecord = true;
 					}
 				}
 			} elseif ($dnsNegativeTtl !== null) {

tests/lib/Http/Client/DnsPinMiddlewareTest.php

@@ -554,10 +554,11 @@ static function (RequestInterface $request, array $options) {
 			['nextcloud' => ['allow_local_address' => false]]
 		);
 
-		$this->assertCount(4, $dnsQueries);
+		$this->assertCount(3, $dnsQueries);
 		$this->assertContains('example.com' . DNS_SOA, $dnsQueries);
 		$this->assertContains('subsubdomain.subdomain.example.com' . DNS_A, $dnsQueries);
 		$this->assertContains('subsubdomain.subdomain.example.com' . DNS_AAAA, $dnsQueries);
-		$this->assertContains('subsubdomain.subdomain.example.com' . DNS_CNAME, $dnsQueries);
+		// CNAME should not be queried if A or AAAA succeeded already
+		$this->assertNotContains('subsubdomain.subdomain.example.com' . DNS_CNAME, $dnsQueries);
 	}
 }