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net: avoid an infinite loop in LookupAddr

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If a request for a PTR record returned a response with a non-PTR
answer, goLookupPTR would loop forever.  Skipping non-PTR answers
guarantees progress through the DNS response.

Fixes #34660

Change-Id: I56f9d21e5342d07e7d843d253267e93a29707904
Reviewed-on: https://go-review.googlesource.com/c/go/+/198460
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Michael Hendricks 2019-10-02 09:30:51 -06:00 • committed by Brad Fitzpatrick
parent e85ffec784
commit f0e940ebc9
2 changed files with 55 additions and 0 deletions
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8
src/net/dnsclient_unix.go
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@ -765,6 +765,14 @@ func (r *Resolver) goLookupPTR(ctx context.Context, addr string) ([]string, erro
}
}
if h.Type != dnsmessage.TypePTR {
err := p.SkipAnswer()
if err != nil {
return nil, &DNSError{
Err: "cannot marshal DNS message",
Name: addr,
Server: server,
}
}
continue
}
ptr, err := p.PTRResource()