fix an unlikely crypto downgrade attack found during audit

if DP3 and earlier protocols are active, a malicious client may intervene
during connect with an authenticated player's connect and downgrade to
unauthenticated NQ protocol

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@11758 d7cf8633-e32d-0410-b094-e92efae38249
::stable-branch::merge=f8174044991f4ebf3a877716ef116e99e45916d6

diff --git a/netconn.c b/netconn.c
index 2147926fb6f5ee7644524b10f0c74e75ad11dfd2..eaf5dbd6545a4c19f7d0fd7e398922fcf1631404 100755 (executable)
--- a/netconn.c
+++ b/netconn.c
@@ -3183,6 +3183,22 @@ static int NetConn_ServerParsePacket(lhnetsocket_t *mysocket, unsigned char *dat
                                        // or coming back from a timeout
                                        // (if so, keep their stuff intact)
 
+                                       crypto_t *crypto = Crypto_ServerGetInstance(peeraddress);
+                                       if((crypto && crypto->authenticated) || client->netconnection->crypto.authenticated)
+                                       {
+                                               if (developer_extra.integer)
+                                                       Con_Printf("Datagram_ParseConnectionless: sending CCREP_REJECT \"Attempt to downgrade crypto.\" to %s.\n", addressstring2);
+                                               SZ_Clear(&sv_message);
+                                               // save space for the header, filled in later
+                                               MSG_WriteLong(&sv_message, 0);
+                                               MSG_WriteByte(&sv_message, CCREP_REJECT);
+                                               MSG_WriteString(&sv_message, "Attempt to downgrade crypto.\n");
+                                               StoreBigLong(sv_message.data, NETFLAG_CTL | (sv_message.cursize & NETFLAG_LENGTH_MASK));
+                                               NetConn_Write(mysocket, sv_message.data, sv_message.cursize, peeraddress);
+                                               SZ_Clear(&sv_message);
+                                               return true;
+                                       }
+
                                        // send a reply
                                        if (developer_extra.integer)
                                                Con_DPrintf("Datagram_ParseConnectionless: sending duplicate CCREP_ACCEPT to %s.\n", addressstring2);