crypto: avoid generating control-like packets

[xonotic/darkplaces.git] / crypto.c

diff --git a/crypto.c b/crypto.c
index 4b9d3976ab29fbb9851b118f79dffc63405c9f3e..7ff8ff48758c7a274c4d3752deacce9667d91a46 100644 (file)
--- a/crypto.c
+++ b/crypto.c
@@ -1309,9 +1309,14 @@ static void seacpy(unsigned char *key, const unsigned char *iv, unsigned char *d
        }
 }
 
+// NOTE: we MUST avoid the following begins of the packet:
+//   1. 0xFF, 0xFF, 0xFF, 0xFF
+//   2. 0x80, 0x00, length/256, length%256
+// this luckily does NOT affect AES mode, where the first byte always is in the range from 0x00 to 0x0F
 const void *Crypto_EncryptPacket(crypto_t *crypto, const void *data_src, size_t len_src, void *data_dst, size_t *len_dst, size_t len)
 {
        unsigned char h[32];
+       int i;
        if(crypto->authenticated)
        {
                if(crypto->use_aes)
@@ -1346,6 +1351,15 @@ const void *Crypto_EncryptPacket(crypto_t *crypto, const void *data_src, size_t
                        *len_dst = len_src + 16;
                        memcpy(data_dst, h, 16);
                        memcpy(((unsigned char *) data_dst) + 16, (unsigned char *) data_src, len_src);
+
+                       // handle the "avoid" conditions:
+                       i = BuffBigLong(data_dst);
+                       if(
+                               (i == (int)0xFFFFFFFF) // avoid QW control packet
+                               ||
+                               (i == (int)0x80000000 + (int)*len_dst) // avoid NQ control packet
+                       )
+                               *(unsigned char *)data_dst ^= 0x80; // this will ALWAYS fix it
                }
                return data_dst;
        }
@@ -1359,6 +1373,17 @@ const void *Crypto_EncryptPacket(crypto_t *crypto, const void *data_src, size_t
 const void *Crypto_DecryptPacket(crypto_t *crypto, const void *data_src, size_t len_src, void *data_dst, size_t *len_dst, size_t len)
 {
        unsigned char h[32];
+       int i;
+
+       // silently handle non-crypto packets
+       i = BuffBigLong(data_src);
+       if(
+               (i == (int)0xFFFFFFFF) // avoid QW control packet
+               ||
+               (i == (int)0x80000000 + (int)len_src) // avoid NQ control packet
+       )
+               return NULL;
+
        if(crypto->authenticated)
        {
                if(crypto->use_aes)
@@ -1413,11 +1438,31 @@ const void *Crypto_DecryptPacket(crypto_t *crypto, const void *data_src, size_t
                                Com_HexDumpToConsole((const unsigned char *) data_src, len_src);
                                return NULL;
                        }
+
                        if(memcmp((const unsigned char *) data_src, h, 16)) // ignore first byte, used for length
                        {
-                               Con_Printf("HMAC mismatch\n");
-                               Com_HexDumpToConsole((const unsigned char *) data_src, len_src);
-                               return NULL;
+                               // undo the "avoid conditions"
+                               if(
+                                               (i == (int)0x7FFFFFFF) // avoided QW control packet
+                                               ||
+                                               (i == (int)0x00000000 + (int)len_src) // avoided NQ control packet
+                                 )
+                               {
+                                       // do the avoidance on the hash too
+                                       h[0] ^= 0x80;
+                                       if(memcmp((const unsigned char *) data_src, h, 16)) // ignore first byte, used for length
+                                       {
+                                               Con_Printf("HMAC mismatch\n");
+                                               Com_HexDumpToConsole((const unsigned char *) data_src, len_src);
+                                               return NULL;
+                                       }
+                               }
+                               else
+                               {
+                                       Con_Printf("HMAC mismatch\n");
+                                       Com_HexDumpToConsole((const unsigned char *) data_src, len_src);
+                                       return NULL;
+                               }
                        }
                        return ((const unsigned char *) data_src) + 16; // no need to copy, so data_dst is not used
                }