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Code Issues Releases Wiki Activity

Fix serve-stale bug when cache has no data

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We recently fixed a bug where in some cases (when following an
expired CNAME for example), named could return SERVFAIL if the target
record is still valid (see isc-projects/bind9#3678, and
isc-projects/bind9!7096). We fixed this by considering non-stale
RRsets as well during the stale lookup.

However, this triggered a new bug because despite the answer from
cache not being stale, the lookup may be triggered by serve-stale.
If the answer from database is not stale, the fix in
isc-projects/bind9!7096 erroneously skips the serve-stale logic.

Add 'answer_found' checks to the serve-stale logic to fix this issue.

(cherry picked from commit bbd163acf67843c76099921e467dd0ef90f3f670)
This commit is contained in:
Matthijs Mekking 2023-04-20 16:22:53 +02:00
parent ad5d447348
commit b90bad93cb
1 changed files with 36 additions and 10 deletions
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46
lib/ns/query.c
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@ -5852,6 +5852,27 @@ query_refresh_rrset(query_ctx_t *orig_qctx) {
qctx_destroy(&qctx);
}
/*%
* Depending on the db lookup result, we can respond to the
* client this stale answer.
*/
static bool
stale_client_answer(isc_result_t result) {
switch (result) {
case ISC_R_SUCCESS:
case DNS_R_EMPTYNAME:
case DNS_R_NXRRSET:
case DNS_R_NCACHENXRRSET:
case DNS_R_CNAME:
case DNS_R_DNAME:
return (true);
default:
return (false);
}
UNREACHABLE();
}
/*%
* Perform a local database lookup, in either an authoritative or
* cache database. If unable to answer, call ns_query_done(); otherwise
@ -5983,7 +6004,6 @@ query_lookup(query_ctx_t *qctx) {
{
/* Found non-stale usable rdataset. */
answer_found = true;
goto gotanswer;
}
if (dbfind_stale || stale_refresh_window || stale_timeout) {
@ -6019,7 +6039,7 @@ query_lookup(query_ctx_t *qctx) {
if (stale_found) {
ns_client_extendederror(qctx->client, ede,
"resolver failure");
} else {
} else if (!answer_found) {
/*
* Resolver failure, no stale data, nothing more we
* can do, return SERVFAIL.
@ -6042,7 +6062,7 @@ query_lookup(query_ctx_t *qctx) {
ns_client_extendederror(
qctx->client, ede,
"query within stale refresh time window");
} else {
} else if (!answer_found) {
/*
* During the stale refresh window explicitly do not try
* to refresh the data, because a recent lookup failed.
@ -6052,7 +6072,7 @@ query_lookup(query_ctx_t *qctx) {
}
} else if (stale_timeout) {
if ((qctx->options & DNS_GETDB_STALEFIRST) != 0) {
if (!stale_found) {
if (!stale_found && !answer_found) {
/*
* We have nothing useful in cache to return
* immediately.
@ -6069,7 +6089,7 @@ query_lookup(query_ctx_t *qctx) {
&qctx->client->query.fetch);
}
return (query_lookup(qctx));
} else {
} else if (stale_client_answer(result)) {
/*
* Immediately return the stale answer, start a
* resolver fetch to refresh the data in cache.
@ -6081,9 +6101,12 @@ query_lookup(query_ctx_t *qctx) {
"refresh the RRset will still be made",
namebuf);
qctx->refresh_rrset = STALE(qctx->rdataset);
ns_client_extendederror(
qctx->client, ede,
"stale data prioritized over lookup");
if (stale_found) {
ns_client_extendederror(
qctx->client, ede,
"stale data prioritized over "
"lookup");
}
}
} else {
/*
@ -6099,7 +6122,11 @@ query_lookup(query_ctx_t *qctx) {
if (stale_found) {
ns_client_extendederror(qctx->client, ede,
"client timeout");
} else {
} else if (!answer_found) {
return (result);
}
if (!stale_client_answer(result)) {
return (result);
}
@ -6112,7 +6139,6 @@ query_lookup(query_ctx_t *qctx) {
}
}
gotanswer:
if (stale_timeout && (answer_found || stale_found)) {
/*
* Mark RRsets that we are adding to the client message on a