BGP: Fix processing of IPv6 Flowspec

During NLRI parsing of IPv6 Flowspec, dst prefix was not properly
extracted from NLRI, therefore a received flow was stored in a different
position in flowspec routing table, and was not reachable by command
'show route <flow>'.

Add proper prefix part accessors to flowspec code and use them from BGP
NLRI parsing code.

Thanks to Alex D. for the bugreport.

lib/flowspec.c

@@ -112,7 +112,6 @@ get_value_length(const byte *op)
 }
 
 
-
 /*
  *	Flowspec iterators
  */
@@ -245,6 +244,45 @@ flow6_next_part(const byte *pos, const byte *end)
 }
 
 
+/*
+ *	Flowspec accessors
+ */
+
+
+static inline ip4_addr
+flow_read_ip4(const byte *px, uint pxlen)
+{
+  ip4_addr ip = IP4_NONE;
+  memcpy(&ip, px, BYTES(pxlen));
+  return ip4_ntoh(ip);
+}
+
+ip4_addr
+flow_read_ip4_part(const byte *part)
+{
+  return flow_read_ip4(part + 2, part[1]);
+}
+
+static inline ip6_addr
+flow_read_ip6(const byte *px, uint pxlen, uint pxoffset)
+{
+  uint floor_offset = BYTES(pxoffset - (pxoffset % 8));
+  uint ceil_len = BYTES(pxlen);
+  ip6_addr ip = IP6_NONE;
+
+  memcpy(((byte *) &ip) + floor_offset, px, ceil_len - floor_offset);
+
+  return ip6_ntoh(ip);
+}
+
+ip6_addr
+flow_read_ip6_part(const byte *part)
+{
+  return flow_read_ip6(part + 3, part[1], part[2]);
+}
+
+
+
 /*
  * 	Flowspec validation
  */
@@ -779,26 +817,6 @@ flow_builder_set_type(struct flow_builder *fb, enum flow_type type)
   fb->this_type = type;
 }
 
-static ip4_addr
-flow_read_ip4(const byte *px, uint pxlen)
-{
-  ip4_addr ip = IP4_NONE;
-  memcpy(&ip, px, BYTES(pxlen));
-  return ip4_ntoh(ip);
-}
-
-static ip6_addr
-flow_read_ip6(const byte *px, uint pxlen, uint pxoffset)
-{
-  uint floor_offset = BYTES(pxoffset - (pxoffset % 8));
-  uint ceil_len = BYTES(pxlen);
-  ip6_addr ip = IP6_NONE;
-
-  memcpy(((byte *) &ip) + floor_offset, px, ceil_len - floor_offset);
-
-  return ip6_ntoh(ip);
-}
-
 static void
 builder_write_parts(struct flow_builder *fb, byte *buf)
 {
@@ -831,9 +849,9 @@ flow_builder4_finalize(struct flow_builder *fb, linpool *lpool)
 
   if (fb->parts[FLOW_TYPE_DST_PREFIX].length)
   {
-    byte *p = fb->data.data + fb->parts[FLOW_TYPE_DST_PREFIX].offset + 1;
+    byte *part = fb->data.data + fb->parts[FLOW_TYPE_DST_PREFIX].offset;
-    pxlen = *p++;
+    prefix = flow_read_ip4_part(part);
-    prefix = flow_read_ip4(p, pxlen);
+    pxlen = part[1];
   }
   *f = NET_ADDR_FLOW4(prefix, pxlen, data_len);
 
@@ -861,10 +879,9 @@ flow_builder6_finalize(struct flow_builder *fb, linpool *lpool)
 
   if (fb->parts[FLOW_TYPE_DST_PREFIX].length)
   {
-    byte *p = fb->data.data + fb->parts[FLOW_TYPE_DST_PREFIX].offset + 1;
+    byte *part = fb->data.data + fb->parts[FLOW_TYPE_DST_PREFIX].offset;
-    pxlen = *p++;
+    prefix = flow_read_ip6_part(part);
-    uint pxoffset = *p++;
+    pxlen = part[1];
-    prefix = flow_read_ip6(p, pxlen, pxoffset);
   }
   *n = NET_ADDR_FLOW6(prefix, pxlen, data_len);
 
@@ -947,18 +964,18 @@ fragment_val_str(u8 val)
 static void
 net_format_flow_ip(buffer *b, const byte *part, int ipv6)
 {
-  uint pxlen = *(part+1);
+  uint pxlen = part[1];
   if (ipv6)
   {
-    uint pxoffset = *(part+2);
+    uint pxoffset = part[2];
     if (pxoffset)
-      buffer_print(b, "%I6/%u offset %u; ", flow_read_ip6(part+3,pxlen,pxoffset), pxlen, pxoffset);
+      buffer_print(b, "%I6/%u offset %u; ", flow_read_ip6_part(part), pxlen, pxoffset);
     else
-      buffer_print(b, "%I6/%u; ", flow_read_ip6(part+3,pxlen,0), pxlen);
+      buffer_print(b, "%I6/%u; ", flow_read_ip6_part(part), pxlen);
   }
   else
   {
-    buffer_print(b, "%I4/%u; ", flow_read_ip4(part+2,pxlen), pxlen);
+    buffer_print(b, "%I4/%u; ", flow_read_ip4_part(part), pxlen);
   }
 }
 

lib/flowspec.h

@@ -85,6 +85,14 @@ const byte *flow4_next_part(const byte *pos, const byte *end);
 const byte *flow6_next_part(const byte *pos, const byte *end);
 
 
+/*
+ *	Flowspec accessors
+ */
+
+ip4_addr flow_read_ip4_part(const byte *part);
+ip6_addr flow_read_ip6_part(const byte *part);
+
+
 /*
  * 	Flowspec Builder
  */

lib/flowspec_test.c

@@ -137,7 +137,7 @@ static int
 t_iterators6(void)
 {
   net_addr_flow6 *f;
-  NET_ADDR_FLOW6_(f, ip6_build(0,0,0x12345678,0x9a000000), 64, ((byte[]) {
+  NET_ADDR_FLOW6_(f, ip6_build(0,0,0x12345678,0x9a000000), 0x68, ((byte[]) {
     26, /* Length */
     FLOW_TYPE_DST_PREFIX, 0x68, 0x40, 0x12, 0x34, 0x56, 0x78, 0x9a,
     FLOW_TYPE_SRC_PREFIX, 0x08, 0x0, 0xc0,
@@ -166,6 +166,56 @@ t_iterators6(void)
   return 1;
 }
 
+static int
+t_accessors4(void)
+{
+  net_addr_flow4 *f;
+  NET_ADDR_FLOW4_(f, ip4_build(5,6,7,0), 24, ((byte[]) {
+    25, /* Length */
+    FLOW_TYPE_DST_PREFIX, 24, 5, 6, 7,
+    FLOW_TYPE_SRC_PREFIX, 32, 10, 11, 12, 13,
+    FLOW_TYPE_IP_PROTOCOL, 0x81, 0x06,
+    FLOW_TYPE_PORT, 0x03, 0x89, 0x45, 0x8b, 0x91, 0x1f, 0x90,
+    FLOW_TYPE_TCP_FLAGS, 0x80, 0x55,
+  }));
+
+  const byte *p1_dst_px		= &f->data[1];
+  const ip4_addr p1_dst_addr	= ip4_build(5,6,7,0);
+
+  const byte *p2_src_px		= &f->data[6];
+  const ip4_addr p2_src_addr	= ip4_build(10,11,12,13);
+
+  bt_assert(ip4_equal(flow_read_ip4_part(p1_dst_px), p1_dst_addr));
+  bt_assert(ip4_equal(flow_read_ip4_part(p2_src_px), p2_src_addr));
+
+  return 1;
+}
+
+static int
+t_accessors6(void)
+{
+  net_addr_flow6 *f;
+  NET_ADDR_FLOW6_(f, ip6_build(0,0,0x12345678,0x9a000000), 0x68, ((byte[]) {
+    26, /* Length */
+    FLOW_TYPE_DST_PREFIX, 0x68, 0x40, 0x12, 0x34, 0x56, 0x78, 0x9a,
+    FLOW_TYPE_SRC_PREFIX, 0x08, 0x0, 0xc0,
+    FLOW_TYPE_NEXT_HEADER, 0x81, 0x06,
+    FLOW_TYPE_PORT, 0x03, 0x89, 0x45, 0x8b, 0x91, 0x1f, 0x90,
+    FLOW_TYPE_LABEL, 0x80, 0x55,
+  }));
+
+  const byte *p1_dst_px		= &f->data[1];
+  const ip6_addr p1_dst_addr	= ip6_build(0,0,0x12345678,0x9a000000);
+
+  const byte *p2_src_px 	= &f->data[9];
+  const ip6_addr p2_src_addr	= ip6_build(0xc0000000, 0, 0, 0);
+
+  bt_assert(ip6_equal(flow_read_ip6_part(p1_dst_px), p1_dst_addr));
+  bt_assert(ip6_equal(flow_read_ip6_part(p2_src_px), p2_src_addr));
+
+  return 1;
+}
+
 static int
 t_validation4(void)
 {
@@ -628,6 +678,8 @@ main(int argc, char *argv[])
   bt_test_suite(t_first_part,   "Searching first part in net_addr_flow");
   bt_test_suite(t_iterators4,   "Testing iterators (IPv4)");
   bt_test_suite(t_iterators6,   "Testing iterators (IPv6)");
+  bt_test_suite(t_accessors4,   "Testing accessors (IPv4)");
+  bt_test_suite(t_accessors6,   "Testing accessors (IPv6)");
   bt_test_suite(t_validation4,  "Testing validation (IPv4)");
   bt_test_suite(t_validation6,  "Testing validation (IPv6)");
   bt_test_suite(t_builder4,     "Inserting components into existing Flow Specification (IPv4)");

proto/bgp/packets.c

@@ -1831,13 +1831,9 @@ bgp_decode_nlri_flow4(struct bgp_parse_state *s, byte *pos, uint len, rta *a)
     }
 
     /* Decode dst prefix */
-    ip4_addr px = IP4_NONE;
+    ip4_addr px = flow_read_ip4_part(data);
     uint pxlen = data[1];
 
-    // FIXME: Use some generic function
-    memcpy(&px, data+2, BYTES(pxlen));
-    px = ip4_and(ip4_ntoh(px), ip4_mkmask(pxlen));
-
     /* Prepare the flow */
     net_addr *n = alloca(sizeof(struct net_addr_flow4) + flen);
     net_fill_flow4(n, px, pxlen, pos, flen);
@@ -1923,13 +1919,9 @@ bgp_decode_nlri_flow6(struct bgp_parse_state *s, byte *pos, uint len, rta *a)
     }
 
     /* Decode dst prefix */
-    ip6_addr px = IP6_NONE;
+    ip6_addr px = flow_read_ip6_part(data);
     uint pxlen = data[1];
 
-    // FIXME: Use some generic function
-    memcpy(&px, data+2, BYTES(pxlen));
-    px = ip6_and(ip6_ntoh(px), ip6_mkmask(pxlen));
-
     /* Prepare the flow */
     net_addr *n = alloca(sizeof(struct net_addr_flow6) + flen);
     net_fill_flow6(n, px, pxlen, pos, flen);