[Spice-devel] [PATCH spice-server 2/3] Prevent integer overflows in capability checks

[Frediano Ziglio]

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 limit the capabilities to 1024
(capabilities are expressed in number of uint32_t items).

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

This patch was developed and reviewed internally for security reasons.

diff --git a/server/reds.c b/server/reds.c
index e7ebc43..953a95a 100644
--- a/server/reds.c
+++ b/server/reds.c
@@ -2186,6 +2186,14 @@ static void reds_handle_read_link_done(void *opaque)
     link_mess->num_channel_caps = GUINT32_FROM_LE(link_mess->num_channel_caps);
     link_mess->num_common_caps = GUINT32_FROM_LE(link_mess->num_common_caps);
 
+    /* Prevent DoS. 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;
+    }
+
     num_caps = link_mess->num_common_caps + link_mess->num_channel_caps;
     caps = (uint32_t *)((uint8_t *)link_mess + link_mess->caps_offset);
 
-- 
2.9.3