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Fix handling of RFC6603 Prefix Exclude Option #151

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Fix handling of RFC6603 Prefix Exclude Option #151

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58 changes: 33 additions & 25 deletions src/dhcpv6.c
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Original file line number Diff line number Diff line change
Expand Up @@ -822,13 +822,15 @@ static void dhcpv6_send(enum dhcpv6_msg req_msg_type, uint8_t trid[3], uint32_t
if (pd_entries[j].iaid != iaid)
continue;

uint8_t ex_len = 0;
if (pd_entries[j].exclusion_length > 0)
ex_len = ((pd_entries[j].exclusion_length - pd_entries[j].length - 1) / 8) + 6;

uint8_t excl_subnet_id_nbits, excl_subnet_id_nbytes, excl_opt_len = 0;
if (pd_entries[j].exclusion_length > 0) {
excl_subnet_id_nbits = pd_entries[j].exclusion_length - pd_entries[j].length;
excl_subnet_id_nbytes = ((excl_subnet_id_nbits - 1) / 8) + 1;
excl_opt_len = excl_subnet_id_nbytes + DHCPV6_OPT_HDR_SIZE + 1;
}
struct dhcpv6_ia_prefix p = {
.type = htons(DHCPV6_OPT_IA_PREFIX),
.len = htons(sizeof(p) - DHCPV6_OPT_HDR_SIZE_U + ex_len),
.len = htons(sizeof(p) - DHCPV6_OPT_HDR_SIZE_U + excl_opt_len),
.prefix = pd_entries[j].length,
.addr = pd_entries[j].target
};
Expand All @@ -841,21 +843,22 @@ static void dhcpv6_send(enum dhcpv6_msg req_msg_type, uint8_t trid[3], uint32_t
memcpy(ia_pd + ia_pd_len, &p, sizeof(p));
ia_pd_len += sizeof(p);

if (ex_len) {
if (excl_opt_len) {
ia_pd[ia_pd_len++] = 0;
ia_pd[ia_pd_len++] = DHCPV6_OPT_PD_EXCLUDE;
ia_pd[ia_pd_len++] = 0;
ia_pd[ia_pd_len++] = ex_len - DHCPV6_OPT_HDR_SIZE;
ia_pd[ia_pd_len++] = excl_opt_len - DHCPV6_OPT_HDR_SIZE;
ia_pd[ia_pd_len++] = pd_entries[j].exclusion_length;

uint32_t excl = ntohl(pd_entries[j].router.s6_addr32[1]);
excl >>= (64 - pd_entries[j].exclusion_length);
excl <<= 8 - ((pd_entries[j].exclusion_length - pd_entries[j].length) % 8);
uint32_t excluded_bits = ntohl(pd_entries[j].router.s6_addr32[1]);
excluded_bits >>= (64 - pd_entries[j].exclusion_length); /* Right align subnet ID bits */
excluded_bits <<= (32 - excl_subnet_id_nbits); /* Left align subnet ID bits */

for (size_t k = ex_len - 5; k > 0; --k, excl >>= 8)
ia_pd[ia_pd_len + k] = excl & 0xff;

ia_pd_len += ex_len - 5;
/* Copy subnet ID bits into the option MSB first */
for (size_t k = 0; k < excl_subnet_id_nbytes; ++k) {
ia_pd[ia_pd_len++] = excluded_bits >> 24;
excluded_bits <<= 8;
}
}

hdr->len = htons(ntohs(hdr->len) + ntohs(p.len) + 4U);
Expand Down Expand Up @@ -1826,9 +1829,10 @@ static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret)

dhcpv6_log_status_code(code, "IA_PREFIX", status_msg, msg_len);
if (ret) *ret = 0; // renewal failed
} else if (stype == DHCPV6_OPT_PD_EXCLUDE && slen > 2) {
} else if (stype == DHCPV6_OPT_PD_EXCLUDE && slen >= 2) {
/* RFC 6603 §4.2 Prefix Exclude option */
uint8_t exclude_length = sdata[0];
uint8_t *excl_subnet_id = &sdata[1];
if (exclude_length > 64)
exclude_length = 64;

Expand All @@ -1837,21 +1841,19 @@ static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret)
continue;
}

uint8_t bytes_needed = ((exclude_length - entry.length - 1) / 8) + 1;
if (slen <= bytes_needed) {
uint8_t excl_subnet_id_nbits = exclude_length - entry.length;
uint8_t excl_subnet_id_nbytes = ((excl_subnet_id_nbits - 1) / 8) + 1;
if ((excl_subnet_id + excl_subnet_id_nbytes) > (sdata + slen)) {
update_state = false;
continue;
}

// this decrements through the ipaddr bytes masking against
// the address in the option until byte 0, the option length field.
uint32_t excluded_bits = 0;
do {
excluded_bits = excluded_bits << 8 | sdata[bytes_needed];
} while (--bytes_needed);

excluded_bits >>= 8 - ((exclude_length - entry.length) % 8);
excluded_bits <<= 64 - exclude_length;
/* Copy subnet ID bits out of the option MSB first */
for(size_t i = 0; i < excl_subnet_id_nbytes; i++)
excluded_bits = (excluded_bits << 8) | excl_subnet_id[i];
excluded_bits >>= (8 * excl_subnet_id_nbytes) - excl_subnet_id_nbits; /* Right align subnet ID bits */
excluded_bits <<= (64 - exclude_length); /* Shift subnet ID bits into the low-order bits of the prefix */

// Re-using router field to hold the prefix
entry.router = entry.target; // base prefix
Expand All @@ -1867,6 +1869,12 @@ static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret)
info("%s/%d preferred %d valid %d",
inet_ntop(AF_INET6, &entry.target, buf, sizeof(buf)),
entry.length, entry.preferred , entry.valid);

if (entry.exclusion_length) {
info("PD_EXCLUDE %s/%d",
inet_ntop(AF_INET6, &entry.router, buf, sizeof(buf)),
entry.exclusion_length);
}
}

entry.priority = 0;
Expand Down