From 0000000000000000000000000000000000000000 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 integer overflows in capability checks

The limits for capabilities are specified using 32 bit unsigned integers.
This could cause possible integer overflows causing buffer overflows.
For instance the sum of num_common_caps and num_caps can be 0 avoiding
additional checks.
As the link message is now capped to 4096 and the capabilities are
contained in the link message, this commit limits the capabilities
to 1024 (capabilities are expressed in number of uint32_t items).

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
---
 server/reds.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/server/reds.c b/server/reds.c
index 86a33d5..c639aa3 100644
--- a/server/reds.c
+++ b/server/reds.c
@@ -2113,6 +2113,14 @@ static void reds_handle_read_link_done(void *opaque)
     num_caps = link_mess->num_common_caps + link_mess->num_channel_caps;
     caps = (uint32_t *)((uint8_t *)link_mess + link_mess->caps_offset);
 
+    /* Prevent integer overflows. Currently we defined only 13 capabilities,
+     * I expect 1024 to be valid for quite a lot time */
+    if (link_mess->num_channel_caps > 1024 || link_mess->num_common_caps > 1024) {
+        reds_send_link_error(link, SPICE_LINK_ERR_INVALID_DATA);
+        reds_link_free(link);
+        return;
+    }
+
     if (num_caps && (num_caps * sizeof(uint32_t) + link_mess->caps_offset >
                      link->link_header.size ||
                      link_mess->caps_offset < sizeof(*link_mess))) {