From 4a0d8cdb05d508cfa9480b54917b93cdd470d1e7 Mon Sep 17 00:00:00 2001
From: Pekka Riikonen <priikone@silcnet.org>
Date: Tue, 16 Dec 2008 17:17:58 +0200
Subject: [PATCH] Packet engine: more padding length check fixes

The padding length must be checked differently depending on whether the
packet is fully encrypted with session key or if only the header is
encrypted with session key (fe. channel messages).
---
 lib/silccore/silcpacket.c | 59 ++++++++++++++++++++++-----------------
 1 file changed, 34 insertions(+), 25 deletions(-)

diff --git a/lib/silccore/silcpacket.c b/lib/silccore/silcpacket.c
index 767ec927..b6715675 100644
--- a/lib/silccore/silcpacket.c
+++ b/lib/silccore/silcpacket.c
@@ -1869,6 +1869,14 @@ static inline void silc_packet_receive_ctr_increment(SilcPacketStream stream,
   SILC_LOG_HEXDUMP(("Counter Block"), iv, 16);
 }
 
+/* Return special packet's encrypted length */
+
+static inline int silc_packet_special_len(unsigned char *data)
+{
+  return (((SilcUInt8)data[4] + (SilcUInt8)data[6] +
+	   (SilcUInt8)data[7] + SILC_PACKET_HEADER_LEN));
+}
+
 /* Decrypts SILC packet.  Handles both normal and special packet decryption.
    Return 0 when packet is normal and 1 when it it special, -1 on error. */
 
@@ -1898,9 +1906,7 @@ static inline int silc_packet_decrypt(SilcCipher cipher, SilcHmac hmac,
       /* Padding length + src id len + dst id len + header length - 16
 	 bytes already decrypted, gives the rest of the encrypted packet */
       silc_buffer_push(buffer, block_len);
-      len = (((SilcUInt8)buffer->data[4] + (SilcUInt8)buffer->data[6] +
-	      (SilcUInt8)buffer->data[7] + SILC_PACKET_HEADER_LEN) -
-	     block_len);
+      len = silc_packet_special_len(buffer->data) - block_len;
       silc_buffer_pull(buffer, block_len);
 
       if (silc_unlikely(len > silc_buffer_len(buffer))) {
@@ -2095,7 +2101,7 @@ static void silc_packet_read_process(SilcPacketStream stream)
   SilcCipher cipher;
   SilcHmac hmac;
   SilcPacket packet;
-  SilcUInt8 sid;
+  SilcUInt8 sid, flags, type;
   SilcUInt16 packetlen;
   SilcUInt32 paddedlen, mac_len, block_len, ivlen, psnlen;
   unsigned char tmp[SILC_PACKET_MIN_HEADER_LEN], *header;
@@ -2197,9 +2203,30 @@ static void silc_packet_read_process(SilcPacketStream stream)
     /* Get packet length and full packet length with padding */
     SILC_PACKET_LENGTH(header, packetlen, paddedlen);
 
+    /* Parse packet header */
+    flags = (SilcPacketFlags)header[2];
+    type = (SilcPacketType)header[3];
+
+    if (stream->sc->engine->local_is_router) {
+      if (type == SILC_PACKET_PRIVATE_MESSAGE &&
+	  (flags & SILC_PACKET_FLAG_PRIVMSG_KEY))
+	normal = FALSE;
+      else if (type != SILC_PACKET_CHANNEL_MESSAGE ||
+	       (type == SILC_PACKET_CHANNEL_MESSAGE &&
+		stream->is_router == TRUE))
+	normal = TRUE;
+    } else {
+      if (type == SILC_PACKET_PRIVATE_MESSAGE &&
+	  (flags & SILC_PACKET_FLAG_PRIVMSG_KEY))
+	normal = FALSE;
+      else if (type != SILC_PACKET_CHANNEL_MESSAGE)
+	normal = TRUE;
+    }
+
     /* Padding sanity checks */
     if (cipher && silc_cipher_get_mode(cipher) != SILC_CIPHER_MODE_CTR &&
-	(paddedlen % block_len) != 0) {
+	((normal && paddedlen % block_len != 0) ||
+	 (!normal && silc_packet_special_len(header) % block_len != 0))) {
       SILC_LOG_DEBUG(("Packet length %d not multiple by cipher block length",
 		      paddedlen));
       silc_mutex_unlock(stream->lock);
@@ -2253,6 +2280,8 @@ static void silc_packet_read_process(SilcPacketStream stream)
       goto out;
     }
     packet->stream = stream;
+    packet->flags = flags;
+    packet->type = type;
 
     /* Allocate more space to packet buffer, if needed */
     if (silc_unlikely(silc_buffer_truelen(&packet->buffer) < paddedlen)) {
@@ -2269,26 +2298,6 @@ static void silc_packet_read_process(SilcPacketStream stream)
       }
     }
 
-    /* Parse packet header */
-    packet->flags = (SilcPacketFlags)header[2];
-    packet->type = (SilcPacketType)header[3];
-
-    if (stream->sc->engine->local_is_router) {
-      if (packet->type == SILC_PACKET_PRIVATE_MESSAGE &&
-	  (packet->flags & SILC_PACKET_FLAG_PRIVMSG_KEY))
-	normal = FALSE;
-      else if (packet->type != SILC_PACKET_CHANNEL_MESSAGE ||
-	       (packet->type == SILC_PACKET_CHANNEL_MESSAGE &&
-		stream->is_router == TRUE))
-	normal = TRUE;
-    } else {
-      if (packet->type == SILC_PACKET_PRIVATE_MESSAGE &&
-	  (packet->flags & SILC_PACKET_FLAG_PRIVMSG_KEY))
-	normal = FALSE;
-      else if (packet->type != SILC_PACKET_CHANNEL_MESSAGE)
-	normal = TRUE;
-    }
-
     SILC_LOG_HEXDUMP(("Incoming packet (%d) len %d",
 		      stream->receive_psn, paddedlen + ivlen + mac_len),
 		     inbuf->data, paddedlen + ivlen + mac_len);
-- 
2.24.0