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bufio: panic in ScanBytes #52351

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catenacyber opened this issue Apr 14, 2022 · 2 comments
Closed

bufio: panic in ScanBytes #52351

catenacyber opened this issue Apr 14, 2022 · 2 comments
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@catenacyber
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What version of Go are you using (go version)?

$ go version
go version go1.17.6 darwin/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="/Users/catena/Library/Caches/go-build"
GOENV="/Users/catena/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/catena/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/catena/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.17.6"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/catena/go/src/github.com/catenacyber/go/src/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/pp/dc1dtf9x2js3v0jx_m010nqr0000gn/T/go-build4237848497=/tmp/go-build -gno-record-gcc-switches -fno-common"
GOROOT/bin/go version: go version go1.17.6 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.17.6
uname -v: Darwin Kernel Version 21.3.0: Wed Jan  5 21:37:58 PST 2022; root:xnu-8019.80.24~20/RELEASE_X86_64
ProductName:	macOS
ProductVersion:	12.2.1
BuildVersion:	21D62
lldb --version: lldb-1316.0.9.41
Apple Swift version 5.6 (swiftlang-5.6.0.323.62 clang-1316.0.20.8)
gdb --version: GNU gdb (GDB) 9.1

What did you do?

Run https://go.dev/play/p/uLom6FqbZYj

What did you expect to see?

The program finishing and printing somme dummy data with an error

What did you see instead?

panic: runtime error: slice bounds out of range [:1] with capacity 0

goroutine 1 [running]:
bufio.ScanBytes(...)
	/usr/local/go-faketime/src/bufio/scan.go:294
main.main()
	/tmp/sandbox1582258977/prog.go:11 +0x1a

Program exited.

Fix could be something like

func ScanBytes(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if len(data) == 0 {
		if atEOF {
			return 0, nil, nil
		} else {
			return 0, nil, io.EOF
		}
	}
	return 1, data[0:1], nil
}

Found by https://github.com/catenacyber/ngolo-fuzzing on oss-fuzz
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=46314
@ianlancetaylor
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ianlancetaylor commented Apr 14, 2022 •
edited

This is not a bug that needs to be fixed. Code is not expected to call ScanBytes directly. The ScanBytes function exists to pass to Scanner.Split. If there is a way to pass ScanBytes to Scanner.Split and then have ScanBytes panic, then that should definitely be fixed. But direct calls of ScanBytes are weird, and are expected to pass valid values. A panic is a reasonable result of calling the function incorrectly.

I'm going to close this issue. Please comment if you disagree.

catenacyber added a commit to catenacyber/ngolo-fuzzing that referenced this issue Apr 14, 2022
@catenacyber
std: exclude bufio.ScanBytes
e7a9048 
cf golang/go#52351
@catenacyber
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Thanks for the explanation

@ianlancetaylor ianlancetaylor mentioned this issue Apr 30, 2022
Closed
@golang golang locked and limited conversation to collaborators Apr 14, 2023
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@ianlancetaylor @gopherbot @catenacyber