lib: Check prefix length from zebra is sensible

* zclient.c: prefix length on router-id and interface address add
  messages not sanity checked.  fix.

* */*_zebra.c: Prefix length on zebra route read was not checked, and
  clients use it to write to storage.  An evil zebra could overflow
  client structures by sending overly long prefixlen.

Prompted by discussions with:

Donald Sharp <sharpd@cumulusnetworks.com>

1 files changed, 28 insertions, 17 deletions

diff --git a/lib/zclient.c b/lib/zclient.c
index 610008b4..d25c8d44 100644
--- a/lib/zclient.c
+++ b/lib/zclient.c
@@ -651,18 +651,30 @@ zebra_redistribute_send (int command, struct zclient *zclient, int type,
   return zclient_send_message(zclient);
 }
 
+/* Get prefix in ZServ format; family should be filled in on prefix */
+static void
+zclient_stream_get_prefix (struct stream *s, struct prefix *p)
+{
+  size_t plen = prefix_blen (p);
+  u_char c;
+  p->prefixlen = 0;
+  
+  if (plen == 0)
+    return;
+  
+  stream_get (&p->u.prefix, s, plen);
+  c = stream_getc(s);
+  p->prefixlen = MIN(plen * 8, c);
+}
+
 /* Router-id update from zebra daemon. */
 void
 zebra_router_id_update_read (struct stream *s, struct prefix *rid)
 {
-  int plen;
-
   /* Fetch interface address. */
   rid->family = stream_getc (s);
-
-  plen = prefix_blen (rid);
-  stream_get (&rid->u.prefix, s, plen);
-  rid->prefixlen = stream_getc (s);
+  
+  zclient_stream_get_prefix (s, rid);
 }
 
 /* Interface addition from zebra daemon. */
@@ -814,8 +826,7 @@ zebra_interface_address_read (int type, struct stream *s, vrf_id_t vrf_id)
   ifindex_t ifindex;
   struct interface *ifp;
   struct connected *ifc;
-  struct prefix p, d;
-  int family;
+  struct prefix p, d, *dp;
   int plen;
   u_char ifc_flags;
 
@@ -840,21 +851,21 @@ zebra_interface_address_read (int type, struct stream *s, vrf_id_t vrf_id)
   ifc_flags = stream_getc (s);
 
   /* Fetch interface address. */
-  family = p.family = stream_getc (s);
-
-  plen = prefix_blen (&p);
-  stream_get (&p.u.prefix, s, plen);
-  p.prefixlen = stream_getc (s);
+  d.family = p.family = stream_getc (s);
+  plen = prefix_blen (&d);
+  
+  zclient_stream_get_prefix (s, &p);
 
   /* Fetch destination address. */
   stream_get (&d.u.prefix, s, plen);
-  d.family = family;
-
+  
+  /* N.B. NULL destination pointers are encoded as all zeroes */
+  dp = memconstant(&d.u.prefix,0,plen) ? NULL : &d;
+  
   if (type == ZEBRA_INTERFACE_ADDRESS_ADD) 
     {
        /* N.B. NULL destination pointers are encoded as all zeroes */
-       ifc = connected_add_by_prefix(ifp, &p,(memconstant(&d.u.prefix,0,plen) ?
-					      NULL : &d));
+       ifc = connected_add_by_prefix(ifp, &p, dp);
        if (ifc != NULL)
 	 {
 	   ifc->flags = ifc_flags;