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>

bgpd/bgp_zebra.c

@@ -607,7 +607,7 @@ zebra_read_ipv4 (int command, struct zclient *zclient, zebra_size_t length,
   /* IPv4 prefix. */
   memset (&p, 0, sizeof (struct prefix_ipv4));
   p.family = AF_INET;
-  p.prefixlen = stream_getc (s);
+  p.prefixlen = MIN(IPV4_MAX_PREFIXLEN, stream_getc (s));
   stream_get (&p.prefix, s, PSIZE (p.prefixlen));
 
   /* Nexthop, ifindex, distance, metric. */
@@ -722,7 +722,7 @@ zebra_read_ipv6 (int command, struct zclient *zclient, zebra_size_t length,
   /* IPv6 prefix. */
   memset (&p, 0, sizeof (struct prefix_ipv6));
   p.family = AF_INET6;
-  p.prefixlen = stream_getc (s);
+  p.prefixlen = MIN(IPV6_MAX_PREFIXLEN, stream_getc (s));
   stream_get (&p.prefix, s, PSIZE (p.prefixlen));
 
   /* Nexthop, ifindex, distance, metric. */

isisd/isis_zebra.c

@@ -570,7 +570,7 @@ isis_zebra_read_ipv4 (int command, struct zclient *zclient,
   api.message = stream_getc (stream);
 
   p.family = AF_INET;
-  p.prefixlen = stream_getc (stream);
+  p.prefixlen = MIN(IPV4_MAX_PREFIXLEN, stream_getc (stream));
   stream_get (&p.prefix, stream, PSIZE (p.prefixlen));
 
   if (CHECK_FLAG (api.message, ZAPI_MESSAGE_NEXTHOP))

lib/zclient.c

@@ -942,18 +942,30 @@ zebra_redistribute_send (int command, struct zclient *zclient, afi_t afi, int ty
   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);
+  zclient_stream_get_prefix (s, rid);
-  stream_get (&rid->u.prefix, s, plen);
-  rid->prefixlen = stream_getc (s);
 }
 
 /* Interface addition from zebra daemon. */
@@ -1263,8 +1275,7 @@ 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;
+  struct prefix p, d, *dp;
-  int family;
   int plen;
   u_char ifc_flags;
 
@@ -1288,24 +1299,24 @@ 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);
+  d.family = p.family = stream_getc (s);
-
+  plen = prefix_blen (&d);
-  plen = prefix_blen (&p);
+  
-  stream_get (&p.u.prefix, s, plen);
+  zclient_stream_get_prefix (s, &p);
-  p.prefixlen = stream_getc (s);
 
   /* 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) 
     {
       ifc = connected_lookup_prefix_exact (ifp, &p);
       if (!ifc)
         {
           /* N.B. NULL destination pointers are encoded as all zeroes */
-          ifc = connected_add_by_prefix(ifp, &p, (memconstant(&d.u.prefix,0,plen) ?
+          ifc = connected_add_by_prefix(ifp, &p, dp);
-					         NULL : &d));
         }
        if (ifc)
 	 {

ospf6d/ospf6_zebra.c

@@ -235,7 +235,7 @@ ospf6_zebra_read_ipv6 (int command, struct zclient *zclient,
   /* IPv6 prefix. */
   memset (&p, 0, sizeof (struct prefix_ipv6));
   p.family = AF_INET6;
-  p.prefixlen = stream_getc (s);
+  p.prefixlen = MIN(IPV6_MAX_PREFIXLEN, stream_getc (s));
   stream_get (&p.prefix, s, PSIZE (p.prefixlen));
 
   /* Nexthop, ifindex, distance, metric. */

ospfd/ospf_zebra.c

@@ -1070,7 +1070,7 @@ ospf_zebra_read_ipv4 (int command, struct zclient *zclient,
   /* IPv4 prefix. */
   memset (&p, 0, sizeof (struct prefix_ipv4));
   p.family = AF_INET;
-  p.prefixlen = stream_getc (s);
+  p.prefixlen = MIN(IPV4_MAX_PREFIXLEN, stream_getc (s));
   stream_get (&p.prefix, s, PSIZE (p.prefixlen));
 
   if (IPV4_NET127(ntohl(p.prefix.s_addr)))

ripd/rip_zebra.c

@@ -153,7 +153,7 @@ rip_zebra_read_ipv4 (int command, struct zclient *zclient, zebra_size_t length,
   /* IPv4 prefix. */
   memset (&p, 0, sizeof (struct prefix_ipv4));
   p.family = AF_INET;
-  p.prefixlen = stream_getc (s);
+  p.prefixlen = MIN(IPV4_MAX_PREFIXLEN, stream_getc (s));
   stream_get (&p.prefix, s, PSIZE (p.prefixlen));
 
   /* Nexthop, ifindex, distance, metric. */

ripngd/ripng_zebra.c

@@ -149,7 +149,7 @@ ripng_zebra_read_ipv6 (int command, struct zclient *zclient,
   /* IPv6 prefix. */
   memset (&p, 0, sizeof (struct prefix_ipv6));
   p.family = AF_INET6;
-  p.prefixlen = stream_getc (s);
+  p.prefixlen = MIN(IPV6_MAX_PREFIXLEN, stream_getc (s));
   stream_get (&p.prefix, s, PSIZE (p.prefixlen));
 
   /* Nexthop, ifindex, distance, metric. */