[Libvir] Fix for buffer overflow in network setup

[Daniel P. Berrange]

There was a buffer overflow in teh code to deal with building command line
arguments which was only exposed when the Fedora RPM builds uses the 
stack protector args to GCC. The attached patch increases the buffer size
and uses snprintf() instead of sprintf().

BTW, if anyone is looking for a patch to write - removing all other calls
to sprintf() would be a worthy task :-)

Regards,
Dan.
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-------------- next part --------------
Index: qemud/conf.c
===================================================================
RCS file: /data/cvs/libvirt/qemud/conf.c,v
retrieving revision 1.43
diff -u -p -r1.43 conf.c
--- qemud/conf.c	16 Mar 2007 15:03:21 -0000	1.43
+++ qemud/conf.c	20 Mar 2007 16:23:54 -0000
@@ -1301,13 +1301,14 @@ int qemudBuildCommandLine(struct qemud_s
     } else {
         int vlan = 0;
         while (net) {
-            char nic[3+1+7+1+17+1];
+            char nic[100];
 
-            sprintf(nic, "nic,macaddr=%02x:%02x:%02x:%02x:%02x:%02x,vlan=%d",
-                    net->mac[0], net->mac[1],
-                    net->mac[2], net->mac[3],
-                    net->mac[4], net->mac[5],
-                    vlan);
+            if (snprintf(nic, sizeof(nic), "nic,macaddr=%02x:%02x:%02x:%02x:%02x:%02x,vlan=%d",
+                         net->mac[0], net->mac[1],
+                         net->mac[2], net->mac[3],
+                         net->mac[4], net->mac[5],
+                         vlan) >= sizeof(nic))
+                goto error;
 
             if (!((*argv)[++n] = strdup("-net")))
                 goto no_memory;