Implement IPv4-Embedded addresses according to RFC6052.

The original algorithm assumed that any prefix length would be valid
and did not skip over bits 64 to 71 and set them to zero.
This means that only dns64 prefixes with length 32 and 96 generated
embedded addresses according to RFC6052, cf. Figure 1 in 2.2.

diff --git a/dns64/dns64.c b/dns64/dns64.c
index 5c70119a54de1711f751f189596b626b19f2d2e0..e7552bb7ddcc2ab3b1d5d21bd0b99a45f3035081 100644 (file)
--- a/dns64/dns64.c
+++ b/dns64/dns64.c
@@ -198,14 +198,17 @@ uitoa(unsigned n, char* s)
 static uint32_t
 extract_ipv4(const uint8_t ipv6[], size_t ipv6_len, const int offset)
 {
-    uint32_t ipv4;
+    uint32_t ipv4 = 0;
+    int i, pos;
     log_assert(ipv6_len == 16); (void)ipv6_len;
-    ipv4 = (uint32_t)ipv6[offset/8+0] << (24 + (offset%8))
-         | (uint32_t)ipv6[offset/8+1] << (16 + (offset%8))
-         | (uint32_t)ipv6[offset/8+2] << ( 8 + (offset%8))
-         | (uint32_t)ipv6[offset/8+3] << ( 0 + (offset%8));
-    if (offset/8+4 < 16)
-        ipv4 |= (uint32_t)ipv6[offset/8+4] >> (8 - offset%8);
+    log_assert(offset == 32 || offset == 40 || offset == 48 || offset == 56 ||
+        offset == 64 || offset == 96);
+    for(i = 0, pos = offset / 8; i < 4; i++, pos++) {
+        if (pos == 8)
+            pos++;
+        ipv4 = ipv4 << 8;
+        ipv4 |= ipv6[pos];
+    }
     return ipv4;
 }
 
@@ -297,17 +300,16 @@ synthesize_aaaa(const uint8_t prefix_addr[], size_t prefix_addr_len,
        size_t aaaa_len)
 {
     log_assert(prefix_addr_len == 16 && a_len == 4 && aaaa_len == 16);
+    log_assert(prefix_net == 32 || prefix_net == 40 || prefix_net == 48 ||
+        prefix_net == 56 || prefix_net == 64 || prefix_net == 96);
+    int i, pos;
     (void)prefix_addr_len; (void)a_len; (void)aaaa_len;
     memcpy(aaaa, prefix_addr, 16);
-    aaaa[prefix_net/8+0] |= a[0] >> (0+prefix_net%8);
-    aaaa[prefix_net/8+1] |= a[0] << (8-prefix_net%8);
-    aaaa[prefix_net/8+1] |= a[1] >> (0+prefix_net%8);
-    aaaa[prefix_net/8+2] |= a[1] << (8-prefix_net%8);
-    aaaa[prefix_net/8+2] |= a[2] >> (0+prefix_net%8);
-    aaaa[prefix_net/8+3] |= a[2] << (8-prefix_net%8);
-    aaaa[prefix_net/8+3] |= a[3] >> (0+prefix_net%8);
-    if (prefix_net/8+4 < 16)  /* <-- my beautiful symmetry is destroyed! */
-    aaaa[prefix_net/8+4] |= a[3] << (8-prefix_net%8);
+    for(i = 0, pos = prefix_net / 8; i < a_len; i++, pos++) {
+        if(pos == 8)
+            aaaa[pos++] = 0;
+        aaaa[pos] = a[i];
+    }
 }
 
 
@@ -374,8 +376,10 @@ dns64_apply_cfg(struct dns64_env* dns64_env, struct config_file* cfg)
         log_err("dns64_prefix is not IPv6: %s", cfg->dns64_prefix);
         return 0;
     }
-    if (dns64_env->prefix_net < 0 || dns64_env->prefix_net > 96) {
-        log_err("dns64-prefix length it not between 0 and 96: %s",
+    if (dns64_env->prefix_net != 32 && dns64_env->prefix_net != 40 &&
+            dns64_env->prefix_net != 48 && dns64_env->prefix_net != 56 &&
+            dns64_env->prefix_net != 64 && dns64_env->prefix_net != 96 ) {
+        log_err("dns64-prefix length it not 32, 40, 48, 56, 64 or 96: %s",
                 cfg->dns64_prefix);
         return 0;
     }