kaspar/RIOT
1
0
Fork 0
mirror of https://github.com/RIOT-OS/RIOT.git synced 2025-12-24 22:13:52 +01:00
Code Releases Activity

gnrc_netif: only use prefix matching as tie-breaker in source selection

Browse Source 
When source address selection is done, both RFC and comments in the code
state, that a longest prefix match should *only* be used as a
tie-breaker between more than one viable candidate. If there is only one
address, there is

a) no need for a tie-breaker
b) in the case of either the destination address or the single remaining
   address being ULAs ([which are considered to be of global scope]
   [RFC4193]) possibly not matching, as `fd00::/7` and e.g. `2001::/8`
   do not have a common prefix.

(b) in fact causes the match function to return -1, causing the source
address selection to return -1, causing the outer function to return the
first address it found (which most often is the link-local address),
causing e.g. a ping to an ULA to fail, even is there is a global
address.

[RFC4193]: https://tools.ietf.org/html/rfc4193
This commit is contained in:
Martine S. Lenders 2019-10-09 17:58:36 +02:00
parent 2458a612b6
commit e787f6b60d
1 changed files with 59 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

66
sys/net/gnrc/netif/gnrc_netif.c
View File

@ -1003,10 +1003,46 @@ static int _create_candidate_set(const gnrc_netif_t *netif,
/* number of "points" assigned to an source address candidate in preferred state */
#define RULE_3_PTS (1)
/**
* @brief Caps the match at a source addresses prefix length
*
* @see https://tools.ietf.org/html/rfc6724#section-2.2
*
* @param[in] netif The network interface @p src was selected from
* @param[in] src A potential source address
* @param[in] match The number of bits matching of @p src with another address
*
* @return @p match or a number lesser than @p match, if @p src has a shorter
* prefix.
*/
static unsigned _cap_match(const gnrc_netif_t *netif, const ipv6_addr_t *src,
unsigned match)
{
unsigned best_prefix = 0;
if (ipv6_addr_is_link_local(src)) {
best_prefix = 64U; /* Link-local prefix is always of length 64 */
}
#ifdef MODULE_GNRC_IPV6_NIB
else {
void *state = NULL;
gnrc_ipv6_nib_pl_t ple;
while (gnrc_ipv6_nib_pl_iter(netif->pid, &state, &ple)) {
if ((ipv6_addr_match_prefix(&ple.pfx, src) > best_prefix)) {
best_prefix = ple.pfx_len;
}
}
}
#endif /* MODULE_GNRC_IPV6_NIB */
return ((best_prefix > 0) && (best_prefix < match)) ? best_prefix : match;
}
static ipv6_addr_t *_src_addr_selection(gnrc_netif_t *netif,
const ipv6_addr_t *dst,
uint8_t *candidate_set)
{
int idx = -1;
/* create temporary set for assigning "points" to candidates winning in the
* corresponding rules.
*/
@ -1081,21 +1117,37 @@ static ipv6_addr_t *_src_addr_selection(gnrc_netif_t *netif,
*/
if (winner_set[i] > max_pts) {
idx = i;
max_pts = winner_set[i];
}
}
/* reset candidate set to mark winners */
memset(candidate_set, 0, (GNRC_NETIF_IPV6_ADDRS_NUMOF + 7) / 8);
/* check if we have a clear winner */
/* check if we have a clear winner, otherwise
* rule 8: Use longest matching prefix.*/
uint8_t best_match = 0;
/* collect candidates with maximum points */
for (int i = 0; i < GNRC_NETIF_IPV6_ADDRS_NUMOF; i++) {
if (winner_set[i] == max_pts) {
bf_set(candidate_set, i);
const ipv6_addr_t *addr = &netif->ipv6.addrs[i];
unsigned match = ipv6_addr_match_prefix(addr, dst);
match = _cap_match(netif, addr, match);
/* if match == 0 for all case, it takes above selected idx */
if (match > best_match) {
idx = i;
best_match = match;
}
}
}
/* otherwise apply rule 8: Use longest matching prefix. */
int idx = _match_to_idx(netif, dst, candidate_set);
return (idx < 0) ? NULL : &netif->ipv6.addrs[idx];
if (idx < 0) {
DEBUG("No winner found\n");
return NULL;
}
else {
DEBUG("Winner is: %s\n", ipv6_addr_to_str(addr_str,
&netif->ipv6.addrs[idx],
sizeof(addr_str)));
return &netif->ipv6.addrs[idx];
}
}
#endif /* MODULE_GNRC_IPV6 */