dix: integer overflow in GetHosts() [CVE-2014-8092 2/4]

GetHosts() iterates over all the hosts it has in memory, and copies
them to a buffer. The buffer length is calculated by iterating over
all the hosts and adding up all of their combined length. There is a
potential integer overflow, if there are lots and lots of hosts (with
a combined length of > ~4 gig). This should be possible by repeatedly
calling ProcChangeHosts() on 64bit machines with enough memory.

This patch caps the list at 1mb, because multi-megabyte hostname
lists for X access control are insane.

v2: backport to nx-libs 3.6.x (Mike DePaulo)
v3: human-readable version of "1 MB" (Mihai Moldovan)
Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

Conflicts:
	os/access.c

1 files changed, 6 insertions, 0 deletions

diff --git a/nx-X11/programs/Xserver/os/access.c b/nx-X11/programs/Xserver/os/access.c
index b6a70a703..532a2f82e 100644
--- a/nx-X11/programs/Xserver/os/access.c
+++ b/nx-X11/programs/Xserver/os/access.c
@@ -1719,6 +1719,10 @@ GetHosts (
     {
 	nHosts++;
 	n += (((host->len + 3) >> 2) << 2) + sizeof(xHostEntry);
+        /* Could check for INT_MAX, but in reality having more than 1mb of
+           hostnames in the access list is ridiculous */
+        if (n >= 1024*1024)
+            break;
     }
     if (n)
     {
@@ -1730,6 +1734,8 @@ GetHosts (
         for (host = validhosts; host; host = host->next)
 	{
 	    len = host->len;
+            if ((ptr + sizeof(xHostEntry) + len) > (data + n))
+                break;
 	    ((xHostEntry *)ptr)->family = host->family;
 	    ((xHostEntry *)ptr)->length = len;
 	    ptr += sizeof(xHostEntry);