From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Sat, 5 Mar 2022 16:06:29 +0000 (+0200)
Subject: dnsdist: Prevent the allocation of a large buffer in NetworkListener::readCB()
X-Git-Tag: dnsdist-1.8.0-rc1~285^2~4
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cd23b326f4d8d1f8b43551b32c60e3f0ea227f7a;p=thirdparty%2Fpdns.git

dnsdist: Prevent the allocation of a large buffer in NetworkListener::readCB()
---

diff --git a/pdns/dnsdistdist/dnsdist-lua-network.cc b/pdns/dnsdistdist/dnsdist-lua-network.cc
index bec50f8d1a..4165025c66 100644
--- a/pdns/dnsdistdist/dnsdist-lua-network.cc
+++ b/pdns/dnsdistdist/dnsdist-lua-network.cc
@@ -35,9 +35,18 @@ NetworkListener::NetworkListener() :
 void NetworkListener::readCB(int desc, FDMultiplexer::funcparam_t& param)
 {
   auto cbData = boost::any_cast<std::shared_ptr<NetworkListener::CBData>>(param);
-  /* reuse ? */
   std::string packet;
-  packet.resize(65535);
+
+#ifdef MSG_TRUNC
+  /* first we peek to avoid allocating a very large buffer. "MSG_TRUNC [...] return the real length of the datagram, even when it was longer than the passed buffer" */
+  auto peeked = recvfrom(desc, nullptr, 0, MSG_PEEK | MSG_TRUNC, nullptr, 0);
+  if (peeked > 0) {
+    packet.resize(static_cast<size_t>(peeked));
+  }
+#endif
+  if (packet.size() == 0) {
+    packet.resize(65535);
+  }
 
   struct sockaddr_un from;
   memset(&from, 0, sizeof(from));