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Fix problem with DNS retries in 2.83/2.84.

Browse Source 
The new logic in 2.83/2.84 which merges distinct requests for the
same domain causes problems with clients which do retries as distinct
requests (differing IDs and/or source ports.) The retries just get
piggy-backed on the first, failed, request.

The logic is now changed so that distinct requests for repeated
queries still get merged into a single ID/source port, but they now
always trigger a re-try upstream.

Thanks to Nicholas Mu for his analysis.
This commit is contained in:
Simon Kelley
2021-02-17 23:56:32 +00:00
parent cfcafdd27c
commit 141a26f979
1 changed files with 43 additions and 36 deletions
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77
src/forward.c
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@@ -278,8 +278,46 @@ static int forward_query(int udpfd, union mysockaddr *udpaddr,
fwd_flags |= FREC_DO_QUESTION;
#endif
/* may be no servers available. */
if (forward || (forward = lookup_frec_by_sender(ntohs(header->id), udpaddr, hash)))
/* Check for retry on existing query from same source */
if (!forward && (!(forward = lookup_frec_by_sender(ntohs(header->id), udpaddr, hash))))
{
/* Maybe query from new source, but the same query may be in progress
from another source. If so, just add this client to the
list that will get the reply.*/
if (!option_bool(OPT_ADD_MAC) && !option_bool(OPT_MAC_B64) &&
(forward = lookup_frec_by_query(hash, fwd_flags)))
{
struct frec_src *new;
/* Note whine_malloc() zeros memory. */
if (!daemon->free_frec_src &&
daemon->frec_src_count < daemon->ftabsize &&
(daemon->free_frec_src = whine_malloc(sizeof(struct frec_src))))
{
daemon->frec_src_count++;
daemon->free_frec_src->next = NULL;
}
/* If we've been spammed with many duplicates, just drop the query. */
if (!daemon->free_frec_src)
return 0;
new = daemon->free_frec_src;
daemon->free_frec_src = new->next;
new->next = forward->frec_src.next;
forward->frec_src.next = new;
new->orig_id = ntohs(header->id);
new->source = *udpaddr;
new->dest = *dst_addr;
new->log_id = daemon->log_id;
new->iface = dst_iface;
new->fd = udpfd;
}
}
/* retry existing query */
if (forward)
{
/* If we didn't get an answer advertising a maximal packet in EDNS,
fall back to 1280, which should work everywhere on IPv6.
@@ -350,39 +388,7 @@ static int forward_query(int udpfd, union mysockaddr *udpaddr,
}
else
{
/* Query from new source, but the same query may be in progress
from another source. If so, just add this client to the
list that will get the reply.*/
if (!option_bool(OPT_ADD_MAC) && !option_bool(OPT_MAC_B64) &&
(forward = lookup_frec_by_query(hash, fwd_flags)))
{
/* Note whine_malloc() zeros memory. */
if (!daemon->free_frec_src &&
daemon->frec_src_count < daemon->ftabsize &&
(daemon->free_frec_src = whine_malloc(sizeof(struct frec_src))))
{
daemon->frec_src_count++;
daemon->free_frec_src->next = NULL;
}
/* If we've been spammed with many duplicates, just drop the query. */
if (daemon->free_frec_src)
{
struct frec_src *new = daemon->free_frec_src;
daemon->free_frec_src = new->next;
new->next = forward->frec_src.next;
forward->frec_src.next = new;
new->orig_id = ntohs(header->id);
new->source = *udpaddr;
new->dest = *dst_addr;
new->log_id = daemon->log_id;
new->iface = dst_iface;
new->fd = udpfd;
}
return 1;
}
/* new query */
if (gotname)
flags = search_servers(now, &addrp, gotname, daemon->namebuff, &type, &domain, &norebind);
@@ -392,6 +398,7 @@ static int forward_query(int udpfd, union mysockaddr *udpaddr,
#endif
type &= ~SERV_DO_DNSSEC;
/* may be no servers available. */
if (daemon->servers && !flags)
forward = get_new_frec(now, NULL, NULL);
/* table full - flags == 0, return REFUSED */