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Apply cache TTL policy to DNAME and synthesized CNAME on wire path (#1418)

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When the scrubber synthesizes a CNAME from a DNAME (authority omits CNAME),
apply cache-min-ttl/cache-max-ttl to both DNAME and synthesized CNAME in
msg_parse so they stay equal and respect config (RFC 6672).

- iterator/iter_scrub.c: In synth_cname_rrset(), clamp TTL to [MIN_TTL,
  MAX_TTL] when !SERVE_ORIGINAL_TTL and write back to both synth CNAME
  and DNAME rrset. Removes FIXME.
This commit is contained in:
Arunabha Das 2026-03-09 18:23:52 +05:30 committed by GitHub
parent 9af29c3ed1
commit 5c6f56f8f1
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GPG key ID: B5690EEEBB952194
1 changed files with 11 additions and 2 deletions
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13
iterator/iter_scrub.c
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@ -285,6 +285,17 @@ synth_cname_rrset(uint8_t** sname, size_t* snamelen, uint8_t* alias,
return NULL;
memmove(cn->rr_first->ttl_data, rrset->rr_first->ttl_data,
sizeof(uint32_t)); /* RFC6672: synth CNAME TTL == DNAME TTL */
/* Apply cache TTL policy so DNAME and synthesized CNAME stay equal
* and respect cache-min-ttl/cache-max-ttl (same as rdata_copy path). */
if(!SERVE_ORIGINAL_TTL) {
uint32_t ttl = sldns_read_uint32(cn->rr_first->ttl_data);
time_t ttl_t = (time_t)ttl;
if(ttl_t < MIN_TTL) ttl_t = MIN_TTL;
if(ttl_t > MAX_TTL) ttl_t = MAX_TTL;
ttl = (uint32_t)ttl_t;
sldns_write_uint32(cn->rr_first->ttl_data, ttl);
sldns_write_uint32(rrset->rr_first->ttl_data, ttl);
}
sldns_write_uint16(cn->rr_first->ttl_data+4, aliaslen);
memmove(cn->rr_first->ttl_data+6, alias, aliaslen);
cn->rr_first->size = sizeof(uint16_t)+aliaslen;
@ -502,8 +513,6 @@ scrub_normalize(sldns_buffer* pkt, struct msg_parse* msg,
log_err("out of memory synthesizing CNAME");
return 0;
}
/* FIXME: resolve the conflict between synthesized
* CNAME ttls and the cache. */
rrset = nx;
continue;