Pull request: 4904 return dhcp msg size

Merge in DNS/adguard-home from 4904-rm-padding to master

Updates #4904.
Updates #4903.

Squashed commit of the following:

commit 85337402ad64395704028534f17ac1887cff64e8
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Sep 9 19:38:09 2022 +0300

    dhcpd: return dhcp msg size

CHANGELOG.md

@@ -15,12 +15,18 @@ and this project adheres to
 ## [v0.108.0] - 2022-12-01 (APPROX.)
 -->
 
+### Changed
+
+- The minimum DHCP message size is reassigned back to BOOTP's constraint of 300
+  bytes ([#4904]).
+
 ### Security
 
 - Weaker cipher suites that use the CBC (cipher block chaining) mode of
   operation have been disabled ([#2993]).
 
 [#2993]: https://github.com/AdguardTeam/AdGuardHome/issues/2993
+[#4904]: https://github.com/AdguardTeam/AdGuardHome/issues/4904
 
 
 

internal/dhcpd/v4.go

@@ -1086,12 +1086,6 @@ func (s *v4Server) packetHandler(conn net.PacketConn, peer net.Addr, req *dhcpv4
 	s.send(peer, conn, req, resp)
 }
 
-// minDHCPMsgSize is the minimum length of the encoded DHCP message in bytes
-// according to RFC-2131.
-//
-// See https://datatracker.ietf.org/doc/html/rfc2131#section-2.
-const minDHCPMsgSize = 576
-
 // send writes resp for peer to conn considering the req's parameters according
 // to RFC-2131.
 //
@@ -1133,16 +1127,6 @@ func (s *v4Server) send(peer net.Addr, conn net.PacketConn, req, resp *dhcpv4.DH
 	}
 
 	pktData := resp.ToBytes()
-	pktLen := len(pktData)
-	if pktLen < minDHCPMsgSize {
-		// Expand the packet to match the minimum DHCP message length.  Although
-		// the dhpcv4 package deals with the BOOTP's lower packet length
-		// constraint, it seems some clients expecting the length being at least
-		// 576 bytes as per RFC 2131 (and an obsolete RFC 1533).
-		//
-		// See https://github.com/AdguardTeam/AdGuardHome/issues/4337.
-		pktData = append(pktData, make([]byte, minDHCPMsgSize-pktLen)...)
-	}
 
 	log.Debug("dhcpv4: sending %d bytes to %s: %s", len(pktData), peer, resp.Summary())