TrueCloudLab/coredns
16
0
Fork 2
Code Issues Pull requests 1 Projects Releases Packages Wiki Activity Actions

cache: do the msg copy right (#4207)

Browse source 
Not sure why this is proving so difficult.. pointers are hard? [Was
tempted to rollback all tweaks here, but the original issue we're fixing
it too important to not have a proper fix].

But we need to make a copy of the message at the earliest point in the
handler because we are changing it (adding an opt rr). If we do this on
the original message (which is a pointer) we change it (obvs). When
undoing those changes we do work on a copy.

Re: testing. There isn't a explicit test for this, so I've added on to
the top-level test/ directory, which indeed makes the issue visible:

master:

~~~
go test -v -run=TestLookupCacheWithoutEdns
=== RUN   TestLookupCacheWithoutEdns
    cache_test.go:154: Expected no OPT RR, but got:
        ;; OPT PSEUDOSECTION:
        ; EDNS: version 0; flags: do; udp: 2048
--- FAIL: TestLookupCacheWithoutEdns (0.01s)
FAIL
~~~

This branch:

~~~
% go test -v -run=TestLookupCacheWithoutEdns
=== RUN   TestLookupCacheWithoutEdns
--- PASS: TestLookupCacheWithoutEdns (0.01s)
PASS
ok  	github.com/coredns/coredns/test	0.109s
~~~

Signed-off-by: Miek Gieben <miek@miek.nl>
This commit is contained in:
Miek Gieben 2020-10-15 16:47:07 +02:00 • committed by GitHub
parent 6938dac21d
commit 268781d355
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
3 changed files with 61 additions and 19 deletions
Download patch file Download diff file Expand all files Collapse all files

14
plugin/cache/handler.go vendored
View file

@ -14,12 +14,13 @@ import (
// ServeDNS implements the plugin.Handler interface.
func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
state := request.Request{W: w, Req: r}
rc := r.Copy() // We potentially modify r, to prevent other plugins from seeing this (r is a pointer), copy r into rc.
state := request.Request{W: w, Req: rc}
do := state.Do()
zone := plugin.Zones(c.Zones).Matches(state.Name())
if zone == "" {
return plugin.NextOrFailure(c.Name(), c.Next, ctx, w, r)
return plugin.NextOrFailure(c.Name(), c.Next, ctx, w, rc)
}
now := c.now().UTC()
@ -39,22 +40,21 @@ func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
}
if i == nil {
if !do {
setDo(r)
setDo(rc)
}
crr := &ResponseWriter{ResponseWriter: w, Cache: c, state: state, server: server, do: do}
return plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, r)
return plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, rc)
}
if ttl < 0 {
servedStale.WithLabelValues(server).Inc()
// Adjust the time to get a 0 TTL in the reply built from a stale item.
now = now.Add(time.Duration(ttl) * time.Second)
go func() {
r := r.Copy()
if !do {
setDo(r)
setDo(rc)
}
crr := &ResponseWriter{Cache: c, state: state, server: server, prefetch: true, remoteAddr: w.LocalAddr(), do: do}
plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, r)
plugin.NextOrFailure(c.Name(), c.Next, ctx, crr, rc)
}()
}
resp := i.toMsg(r, now, do)