bufio: calling Reset with itself leads to infinite recursion #58423
Description
What version of Go are you using (go version)?
$ go version go version go1.20 darwin/arm64
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="arm64" GOBIN="" GOCACHE="/Users/REDACTED/Library/Caches/go-build" GOENV="/Users/REDACTED/Library/Application Support/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="arm64" GOHOSTOS="darwin" GOINSECURE="" GOMODCACHE="/Users/REDACTED/go/pkg/mod" GONOPROXY="REDACTED" GONOSUMDB="REDACTED" GOOS="darwin" GOPATH="/Users/REDACTED/go" GOPRIVATE="REDACTED" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/go/pkg/tool/darwin_arm64" GOVCS="" GOVERSION="go1.20" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/dev/null" 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 -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/p4/t2ydl1qj10s99sfykmbnp6cc0000gq/T/go-build2269043344=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
I ran into this issue in a prometheus package that I was using.
The problem is that bufio.NewReader will return its given io.Reader as-is, if it happens to already be a *bufio.Reader of sufficient size. If you later call bufio.(*Reader).Reset on the "new" *bufio.Reader with the original io.Reader, it ends up setting the *bufio.Reader as its own underlying io.Reader. Then when you try to Read from it, there's an infinite recursion and stack overflow.
It's kinda strange to Reset a *bufio.Reader with the same io.Reader from which it was created, but I don't think bufio.NewReader should use the return as-is optimization without also handling this Reset with self issue.
My repro code is obviously contrived, but the actual case where this happened seemed fairly reasonable.
https://go.dev/play/p/2UTNBLVR1J__E
What did you expect to see?
I expected to see my server running smoothly.
What did you see instead?
My server kept crashing or getting OOM killed.