From 198ad1ea078c1b74c9e24617c509c6a408eb822e Mon Sep 17 00:00:00 2001

From: Frediano Ziglio <fziglio@redhat.com>

Date: Mon, 28 Nov 2016 13:15:58 +0000

Subject: [PATCH] Prevent possible DoS attempts during protocol handshake

The limit for link message is specified using a 32 bit unsigned integer.

This could cause possible DoS due to excessive memory allocations and

some possible crashes.

For instance a value >= 2^31 causes a spice_assert to be triggered in

async_read_handler (reds-stream.c) due to an integer overflow at this

line:

   int n = async->end - async->now;

This could be easily triggered with a program like

  #!/usr/bin/env python

  import socket

  import time

  from struct import pack

  server = '127.0.0.1'

  port = 5900

  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

  s.connect((server, port))

  data = pack('<4sIII', 'REDQ', 2, 2, 0xaaaaaaaa)

  s.send(data)

  time.sleep(1)

without requiring any authentication (the same can be done

with TLS).

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>

---

 server/reds.c | 11 ++++++++++-

 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/server/reds.c b/server/reds.c

index 9e1d5e7..1c215ed 100644

--- a/server/reds.c

+++ b/server/reds.c

@@ -2826,7 +2826,8 @@ static void reds_handle_read_header_done(void *opaque)

     reds->peer_minor_version = header->minor_version;

-    if (header->size < sizeof(SpiceLinkMess)) {

+    /* the check for 4096 is to avoid clients to cause arbitrary big memory allocations */

+    if (header->size < sizeof(SpiceLinkMess) || header->size > 4096) {

         reds_send_link_error(link, SPICE_LINK_ERR_INVALID_DATA);

         spice_warning("bad size %u", header->size);

         reds_link_free(link);

-- 

2.9.3