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fix: DNS NCACHE TTL and OPT RRs (#2900)

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* Fix: DNS NCACHE TTL and OPT RRs

1. DNS NCACHE was not correctly implemented.
2. OPT RRs must not be cached or forwarded.

Closes #2889.
This commit is contained in:
Jiahao Lu 2023-10-16 09:21:06 +08:00 committed by wwqgtxx
parent 9f530525d7
commit 81bbbe4eec
2 changed files with 28 additions and 25 deletions
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6
dns/resolver.go
View file

@ -195,7 +195,11 @@ func (r *Resolver) exchangeWithoutCache(ctx context.Context, m *D.Msg) (msg *D.M
msg := result.(*D.Msg)
if cache {
putMsgToCache(r.lruCache, q.String(), msg)
// OPT RRs MUST NOT be cached, forwarded, or stored in or loaded from master files.
msg.Extra = lo.Filter(msg.Extra, func(rr D.RR, index int) bool {
return rr.Header().Rrtype != D.TypeOPT
})
putMsgToCache(r.lruCache, q.String(), q, msg)
}
}()

41
dns/util.go
View file

@ -29,14 +29,16 @@ const (
MaxMsgSize = 65535
)
const serverFailureCacheTTL uint32 = 5
func minimalTTL(records []D.RR) uint32 {
minObj := lo.MinBy(records, func(r1 D.RR, r2 D.RR) bool {
rr := lo.MinBy(records, func(r1 D.RR, r2 D.RR) bool {
return r1.Header().Ttl < r2.Header().Ttl
})
if minObj != nil {
return minObj.Header().Ttl
}
if rr == nil {
return 0
}
return rr.Header().Ttl
}
func updateTTL(records []D.RR, ttl uint32) {
@ -49,28 +51,25 @@ func updateTTL(records []D.RR, ttl uint32) {
}
}
func putMsgToCache(c *cache.LruCache[string, *D.Msg], key string, msg *D.Msg) {
putMsgToCacheWithExpire(c, key, msg, 0)
}
func putMsgToCacheWithExpire(c *cache.LruCache[string, *D.Msg], key string, msg *D.Msg, sec uint32) {
if sec == 0 {
if sec = minimalTTL(msg.Answer); sec == 0 {
if sec = minimalTTL(msg.Ns); sec == 0 {
sec = minimalTTL(msg.Extra)
}
}
if sec == 0 {
func putMsgToCache(c *cache.LruCache[string, *D.Msg], key string, q D.Question, msg *D.Msg) {
// skip dns cache for acme challenge
if q.Qtype == D.TypeTXT && strings.HasPrefix(q.Name, "_acme-challenge.") {
log.Debugln("[DNS] dns cache ignored because of acme challenge for: %s", q.Name)
return
}
if sec > 120 {
sec = 120 // at least 2 minutes to cache
var ttl uint32
if msg.Rcode == D.RcodeServerFailure {
// [...] a resolver MAY cache a server failure response.
// If it does so it MUST NOT cache it for longer than five (5) minutes [...]
ttl = serverFailureCacheTTL
} else {
ttl = minimalTTL(append(append(msg.Answer, msg.Ns...), msg.Extra...))
}
if ttl == 0 {
return
}
c.SetWithExpire(key, msg.Copy(), time.Now().Add(time.Duration(sec)*time.Second))
c.SetWithExpire(key, msg.Copy(), time.Now().Add(time.Duration(ttl)*time.Second))
}
func setMsgTTL(msg *D.Msg, ttl uint32) {