net: high cpu usage in extractExtendedRCode

[long-name-let-people-remember-you]

Go version

go 1.22.2 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN='/usr/local/go/bin'
GOCACHE='/home/xx/.cache/go-build'
GOENV='/home/xx/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/xx/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/xx/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.2'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/xx/gopath/dns/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build185933323=/tmp/go-build -gno-record-gcc-switches'

What did you do?

concurrent calls to net.LookupAddr

What did you see happen?

pprof seems that goLookupIp may causes high cpu usage



profile.zip

What did you expect to see?

Occasionally, I don’t know what domain name it was when it happened.

[ianlancetaylor]

This code is processing DNS packets. It would help to know what DNS names are being looked up.

That said, at least part of the problem is that methods like dnsmessage.Parser.AdditionalHeader return a value of type ResourceHeader which is 268 bytes on amd64. That's why so much time is being spent in duffcopy.

Still, it should only be an issue if the DNS server is returning a lot of additional headers. It's not clear why that would be happening.

We started looking at the additional headers in https://go.dev/cl/514835. CC @mateusz834

[mateusz834]

Yep, this looks like a DNS response with a bunch of Additional resources, it would be helpful if you could provide us with the raw DNS message reply.

[cagedmantis]

@neild

[gopherbot]

Change https://go.dev/cl/578375 mentions this issue: net: check SkipAdditional error result

[rolandshoemaker]

@gopherbot please open backport issues, this is a PUBLIC track security issue.

[gopherbot]

Backport issue(s) opened: #67039 (for 1.21), #67040 (for 1.22).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gopherbot]

Change https://go.dev/cl/581816 mentions this issue: [release-branch.go1.22] net: check SkipAdditional error result

[gopherbot]

Change https://go.dev/cl/581815 mentions this issue: [release-branch.go1.21] net: check SkipAdditional error result