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abursavich opened this issue Feb 9, 2023 · 4 comments
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bufio: calling Reset with itself leads to infinite recursion #58423

abursavich opened this issue Feb 9, 2023 · 4 comments
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@abursavich
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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.
@ianlancetaylor ianlancetaylor changed the title bufio: infinite recursion in Reader bufio: calling Reset with itself leads to infinite recursion Feb 9, 2023
@gopherbot
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Change https://go.dev/cl/466815 mentions this issue: bufio: permit r.Reset(r) without infinite recursion

@ericlagergren
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@ianlancetaylor you might want to use the two-value type assertion in case r isn't comparable. (Sorry for commenting on a closed issue.)

@ianlancetaylor
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@ericlagergren Thanks, but it's not necessary. When comparing a non-interface against an interface value, we first check that the types are the same. If they are not, the comparison is not-equal. Only if the types are the same do we compare the values. And if the types are the same, we know that the type must be *Reader, which is comparable.

@ericlagergren
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@ianlancetaylor oops. Apologies for the noise.

johanbrandhorst pushed a commit to Pryz/go that referenced this issue Feb 12, 2023
@ianlancetaylor @johanbrandhorst
bufio: permit r.Reset(r) without infinite recursion
cdbae90 
This can happen in reasonable code because NewReader(r) can return r,
if r is already a Reader.

Similarly for Writer.

Fixes golang#58423

Change-Id: Iff9d9265410bee68fbaeb7175369847bd737eb2c
Reviewed-on: https://go-review.googlesource.com/c/go/+/466815
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
@golang golang locked and limited conversation to collaborators Feb 12, 2024
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@abursavich @ianlancetaylor @ericlagergren @gopherbot