Flowspec: Fix IPv6 prefix when offset is not multiple of 8

Current implementation handles flowspec prefix length and offset only
in bytes, but RFC 8956 (Dissemination of Flow Specification Rules for
IPv6) Section 3.1 [1] and example in Section 3.8.2 [2] states the
pattern should begin right after offset *bits*.

For example, pattern "::1:1234:5678:9800:0/60-104" is currently
serialized as "02 68 3c 01 12 34 56 78 98", but it should shift its
pattern 4 more bits to the left: "02 68 3c 11 23 45 67 89 80".

This patch implements shifting left/right for IPv6 type and use it to
correct the behaviour. Test data are replaced with the correct ones.

Minor changes and test vectors done by committer.

[1]: https://www.rfc-editor.org/rfc/rfc8956.html#section-3.1
[2]: https://www.rfc-editor.org/rfc/rfc8956.html#section-3.8.2

lib/flowspec.c

@@ -293,13 +293,9 @@ flow_read_ip4_part(const byte *part)
 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);
+  memcpy(&ip, px, BYTES(pxlen - pxoffset));
+  return ip6_shift_right(ip6_ntoh(ip), pxoffset);
 }
 
 ip6_addr
@@ -476,7 +472,7 @@ flow_validate(const byte *nlri, uint len, int ipv6)
         uint pxoffset = *pos++;
         if (pxoffset > IP6_MAX_PREFIX_LENGTH || pxoffset > pxlen)
           return FLOW_ST_EXCEED_MAX_PREFIX_OFFSET;
-        bytes -= pxoffset / 8;
+        bytes = BYTES(pxlen - pxoffset);
       }
       pos += bytes;
 
@@ -749,12 +745,12 @@ flow_builder6_add_pfx(struct flow_builder *fb, const net_addr_ip6 *n6, u32 pxoff
   if (!builder_add_prepare(fb))
     return 0;
 
-  ip6_addr ip6 = ip6_hton(n6->prefix);
+  ip6_addr ip6 = ip6_hton(ip6_shift_left(n6->prefix, pxoffset));
 
   BUFFER_PUSH(fb->data) = fb->this_type;
   BUFFER_PUSH(fb->data) = n6->pxlen;
   BUFFER_PUSH(fb->data) = pxoffset;
-  push_pfx_to_buffer(fb, BYTES(n6->pxlen) - (pxoffset / 8), ((byte *) &ip6) + (pxoffset / 8));
+  push_pfx_to_buffer(fb, BYTES(n6->pxlen - pxoffset), ((byte *) &ip6));
 
   builder_add_finish(fb);
   return 1;

lib/flowspec_test.c

@@ -542,7 +542,7 @@ t_builder6(void)
 
   const net_addr_flow6 *expect = NET_ADDR_FLOW6_NLRI(
     0,
-    FLOW_TYPE_DST_PREFIX, 103, 61, 0x01, 0x12, 0x34, 0x56, 0x78, 0x98,
+    FLOW_TYPE_DST_PREFIX, 103, 61, 0x22, 0x46, 0x8a, 0xcf, 0x13, 0x00,
     FLOW_TYPE_SRC_PREFIX, 8, 0, 0xc0,
     FLOW_TYPE_NEXT_HEADER, 0x80, 0x06,
     FLOW_TYPE_PORT, 0x03, 0x89, 0x45, 0x8b, 0x91, 0x1f, 0x90,
@@ -678,7 +678,7 @@ t_formatting6(void)
   expect[0] = "flow6 { dst ::1:1234:5678:9800:0/103 offset 61; src c000::/8; next header 6; port 20..40,273; label < 500000; }";
   input[0] = NET_ADDR_FLOW6_NLRI(
     0,
-    FLOW_TYPE_DST_PREFIX, 103, 61, 0x01, 0x12, 0x34, 0x56, 0x78, 0x98,
+    FLOW_TYPE_DST_PREFIX, 103, 61, 0x22, 0x46, 0x8a, 0xcf, 0x13, 0x00,
     FLOW_TYPE_SRC_PREFIX, 8, 0, 0xc0,
     FLOW_TYPE_NEXT_HEADER, 0x81, 0x06,
     FLOW_TYPE_PORT, 0x03, 20, 0x45, 40, 0x91, 0x01, 0x11,

lib/ip.c

@@ -156,6 +156,54 @@ ip6_classify(ip6_addr *a)
 }
 
 
+/*
+ *	IPv6 bit shifting
+ */
+
+ip6_addr
+ip6_shift_left(ip6_addr a, uint bits)
+{
+  if (bits == 0)
+    return a;
+
+  if (bits > 127)
+    return IP6_NONE;
+
+  int words = bits / 32;
+  int rem = bits % 32;
+
+  for (int i = 0; i < 3 - words; i++)
+    a.addr[i] = (a.addr[i + words] << rem) |
+      (rem ? (a.addr[i + words + 1] >> (32 - rem)) : 0);
+
+  a.addr[3 - words] = a.addr[3] << rem;
+  memset(&a.addr[4 - words], 0, words * 4);
+
+  return a;
+}
+
+ip6_addr
+ip6_shift_right(ip6_addr a, uint bits)
+{
+  if (bits == 0)
+    return a;
+
+  if (bits > 127)
+    return IP6_NONE;
+
+  int words = bits / 32;
+  int rem = bits % 32;
+
+  for (int i = 3; i > words; i--)
+    a.addr[i] = (a.addr[i - words] >> rem) |
+      (rem ? (a.addr[i - words - 1] << (32 - rem)) : 0);
+
+  a.addr[words] = a.addr[0] >> rem;
+  memset(&a.addr[0], 0, words * 4);
+
+  return a;
+}
+
 
 /*
  *  Conversion of IPv6 address to presentation format and vice versa.

lib/ip.h

@@ -354,6 +354,9 @@ static inline ip4_addr ip4_setbits(ip4_addr a, uint pos, uint val)
 static inline ip6_addr ip6_setbits(ip6_addr a, uint pos, uint val)
 { a.addr[pos / 32] |= val << (31 - pos % 32); return a; }
 
+ip6_addr ip6_shift_left(ip6_addr a, uint bits);
+ip6_addr ip6_shift_right(ip6_addr a, uint bits);
+
 
 static inline ip4_addr ip4_opposite_m1(ip4_addr a)
 { return _MI4(_I(a) ^ 1); }

lib/ip_test.c

@@ -231,6 +231,66 @@ t_ip6_prefix_equal(void)
   return 1;
 }
 
+static int
+t_ip6_shift_left(void)
+{
+  ip6_addr a = ip6_build(0x8D0D8BDC, 0x1F04DB92, 0xE5117673, 0x70E54449);
+
+  struct { int n; ip6_addr val; } test_vectors[] = {
+      0, ip6_build(0x8D0D8BDC, 0x1F04DB92, 0xE5117673, 0x70E54449),
+      9, ip6_build(0x1B17B83E, 0x09B725CA, 0x22ECE6E1, 0xCA889200),
+     18, ip6_build(0x2F707C13, 0x6E4B9445, 0xD9CDC395, 0x11240000),
+     27, ip6_build(0xE0F826DC, 0x97288BB3, 0x9B872A22, 0x48000000),
+     36, ip6_build(0xF04DB92E, 0x51176737, 0x0E544490, 0x00000000),
+     45, ip6_build(0x9B725CA2, 0x2ECE6E1C, 0xA8892000, 0x00000000),
+     54, ip6_build(0xE4B9445D, 0x9CDC3951, 0x12400000, 0x00000000),
+     63, ip6_build(0x7288BB39, 0xB872A224, 0x80000000, 0x00000000),
+     72, ip6_build(0x11767370, 0xE5444900, 0x00000000, 0x00000000),
+     81, ip6_build(0xECE6E1CA, 0x88920000, 0x00000000, 0x00000000),
+     90, ip6_build(0xCDC39511, 0x24000000, 0x00000000, 0x00000000),
+     99, ip6_build(0x872A2248, 0x00000000, 0x00000000, 0x00000000),
+    108, ip6_build(0x54449000, 0x00000000, 0x00000000, 0x00000000),
+    117, ip6_build(0x89200000, 0x00000000, 0x00000000, 0x00000000),
+    126, ip6_build(0x40000000, 0x00000000, 0x00000000, 0x00000000),
+    128, ip6_build(0x00000000, 0x00000000, 0x00000000, 0x00000000),
+  };
+
+  for (uint i = 0; i < ARRAY_SIZE(test_vectors); i++)
+    bt_assert(ip6_equal(ip6_shift_left(a, test_vectors[i].n), test_vectors[i].val));
+
+  return 1;
+}
+
+static int
+t_ip6_shift_right(void)
+{
+  ip6_addr a = ip6_build(0x8D0D8BDC, 0x1F04DB92, 0xE5117673, 0x70E54449);
+
+  struct { int n; ip6_addr val; } test_vectors[] = {
+      0, ip6_build(0x8D0D8BDC, 0x1F04DB92, 0xE5117673, 0x70E54449),
+      9, ip6_build(0x004686C5, 0xEE0F826D, 0xC97288BB, 0x39B872A2),
+     18, ip6_build(0x00002343, 0x62F707C1, 0x36E4B944, 0x5D9CDC39),
+     27, ip6_build(0x00000011, 0xA1B17B83, 0xE09B725C, 0xA22ECE6E),
+     36, ip6_build(0x00000000, 0x08D0D8BD, 0xC1F04DB9, 0x2E511767),
+     45, ip6_build(0x00000000, 0x0004686C, 0x5EE0F826, 0xDC97288B),
+     54, ip6_build(0x00000000, 0x00000234, 0x362F707C, 0x136E4B94),
+     63, ip6_build(0x00000000, 0x00000001, 0x1A1B17B8, 0x3E09B725),
+     72, ip6_build(0x00000000, 0x00000000, 0x008D0D8B, 0xDC1F04DB),
+     81, ip6_build(0x00000000, 0x00000000, 0x00004686, 0xC5EE0F82),
+     90, ip6_build(0x00000000, 0x00000000, 0x00000023, 0x4362F707),
+     99, ip6_build(0x00000000, 0x00000000, 0x00000000, 0x11A1B17B),
+    108, ip6_build(0x00000000, 0x00000000, 0x00000000, 0x0008D0D8),
+    117, ip6_build(0x00000000, 0x00000000, 0x00000000, 0x00000468),
+    126, ip6_build(0x00000000, 0x00000000, 0x00000000, 0x00000002),
+    128, ip6_build(0x00000000, 0x00000000, 0x00000000, 0x00000000),
+  };
+
+  for (uint i = 0; i < ARRAY_SIZE(test_vectors); i++)
+    bt_assert(ip6_equal(ip6_shift_right(a, test_vectors[i].n), test_vectors[i].val));
+
+  return 1;
+}
+
 int
 main(int argc, char *argv[])
 {
@@ -242,6 +302,8 @@ main(int argc, char *argv[])
   bt_test_suite(t_ip6_ntop, "Converting ip6_addr struct to IPv6 string");
   bt_test_suite(t_ip4_prefix_equal, "Testing ip4_prefix_equal()");
   bt_test_suite(t_ip6_prefix_equal, "Testing ip6_prefix_equal()");
+  bt_test_suite(t_ip6_shift_left, "Testing ip6_shift_left()");
+  bt_test_suite(t_ip6_shift_right, "Testing ip6_shift_right()");
 
   return bt_exit_value();
 }