net: Interface.MTU is an int, but on 32-bit windows the MTU size can be >2 GiB

[YouROK]

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

go version go1.17 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=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/yourok/.cache/go-build"
GOENV="/home/yourok/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/yourok/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/yourok/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17"
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-build3437785326=/tmp/go-build -gno-record-gcc-switches"

In net.Interface MTU int, but in windows 32 bit the mtu size is sometimes more than 2 gb on loopback and the MTU value is negative.

go/src/net/interface.go

Line 33 in 3bbc823

MTU int // maximum transmission unit

[mknyszek]

CC @neild

I suspect there isn't really much we can do about this. MTU probably shouldn't have been an int if this case is possible, but I don't think it's possible to change it now, to follow the Go 1 backwards compatibility guarantee.

[bcmills]

Time to add an MTU64 field? 🤷‍♂️

[neild]

If nothing else, we should saturate MTU to maxint rather than overflowing.