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Apply floor of 60s to TTL of DNSKEY and DS records in cache.

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Short TTLs and specifically zero TTLs can mess up DNSSEC validation.
This commit is contained in:
Simon Kelley
2020-07-12 17:43:25 +01:00
parent 9beb4d9ea2
commit 7e194a0a7d
2 changed files with 18 additions and 4 deletions
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19
src/cache.c
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@@ -472,11 +472,24 @@ void cache_start_insert(void)
struct crec *cache_insert(char *name, union all_addr *addr, unsigned short class, struct crec *cache_insert(char *name, union all_addr *addr, unsigned short class,
time_t now, unsigned long ttl, unsigned int flags) time_t now, unsigned long ttl, unsigned int flags)
{ {
/* Don't log DNSSEC records here, done elsewhere */ #ifdef HAVE_DNSSEC
if (flags & (F_IPV4 | F_IPV6 | F_CNAME | F_SRV)) if (flags & (F_DNSKEY | F_DS))
{ {
/* The DNSSEC validation process works by getting needed records into the
cache, then retrying the validation until they are all in place.
This can be messed up by very short TTLs, and _really_ messed up by
zero TTLs, so we force the TTL to be at least long enough to do a validation.
Ideally, we should use some kind of reference counting so that records are
locked until the validation that asked for them is complete, but this
is much easier, and just as effective. */
if (ttl < DNSSEC_MIN_TTL)
ttl = DNSSEC_MIN_TTL;
}
else
#endif
{
/* Don't log DNSSEC records here, done elsewhere */
log_query(flags | F_UPSTREAM, name, addr, NULL); log_query(flags | F_UPSTREAM, name, addr, NULL);
/* Don't mess with TTL for DNSSEC records. */
if (daemon->max_cache_ttl != 0 && daemon->max_cache_ttl < ttl) if (daemon->max_cache_ttl != 0 && daemon->max_cache_ttl < ttl)
ttl = daemon->max_cache_ttl; ttl = daemon->max_cache_ttl;
if (daemon->min_cache_ttl != 0 && daemon->min_cache_ttl > ttl) if (daemon->min_cache_ttl != 0 && daemon->min_cache_ttl > ttl)

1
src/config.h
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@@ -40,6 +40,7 @@
#define DHCP_PACKET_MAX 16384 /* hard limit on DHCP packet size */ #define DHCP_PACKET_MAX 16384 /* hard limit on DHCP packet size */
#define SMALLDNAME 50 /* most domain names are smaller than this */ #define SMALLDNAME 50 /* most domain names are smaller than this */
#define CNAME_CHAIN 10 /* chains longer than this atr dropped for loop protection */ #define CNAME_CHAIN 10 /* chains longer than this atr dropped for loop protection */
#define DNSSEC_MIN_TTL 60 /* DNSKEY and DS records in cache last at least this long */
#define HOSTSFILE "/etc/hosts" #define HOSTSFILE "/etc/hosts"
#define ETHERSFILE "/etc/ethers" #define ETHERSFILE "/etc/ethers"
#define DEFLEASE 3600 /* default lease time, 1 hour */ #define DEFLEASE 3600 /* default lease time, 1 hour */