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net/http: request with a + in Content-Length is considered valid #39017

@juliens

Description

@juliens

What version of Go are you using (go version)?

$ go version
go version go1.14.2 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/juliens/.cache/go-build"
GOENV="/home/juliens/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GOOS="linux"
GOPATH="/home/juliens/dev/go"
GOPRIVATE=""
GOPROXY="direct"
GOROOT="/home/juliens/go-current"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/juliens/go-current/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build262375258=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I launch a server using

http.ListenAndServe(":8080", http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
    fmt.Println(req.ContentLength)
}))

and after that, I make a call with a Content-Length: +3

echo -ne "POST / HTTP/1.1\r\nContent-Length: +3\r\nHost: 127.0.0.1\r\n\r\naaa\r\n" | nc 127.0.0.1 8083

What did you expect to see?

A bad request ( because of the RFC https://tools.ietf.org/html/rfc2616#section-14.13 )

What did you see instead?

A valid request, the Content-Length is parsed as just 3

More

For what I saw, it's because the Content-Length is parsed by using strconv.ParseInt and so +3 is valid and becomes 3

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