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strconv: index out of range in FormatFloat #52187

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catenacyber opened this issue Apr 6, 2022 · 5 comments
Open

strconv: index out of range in FormatFloat #52187

catenacyber opened this issue Apr 6, 2022 · 5 comments
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@catenacyber
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@catenacyber catenacyber commented Apr 6, 2022

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/tGb3ISbthgv

What did you expect to see?

The program finishing and printing somme dummy data

What did you see instead?

panic: runtime error: index out of range [-1]

goroutine 1 [running]:
strconv.formatDecimal(0x41196f?, 0x7f25fd803500?, 0x0?, 0x0?, 0x7f25fd9fffff?)
	/usr/local/go-faketime/src/strconv/ftoaryu.go:219 +0x278
strconv.ryuFtoaFixed64(0xc000070e80, 0x7f25fd803500?, 0xc00003c5e0?, 0x0)
	/usr/local/go-faketime/src/strconv/ftoaryu.go:154 +0x1c5
strconv.genericFtoa({0xc000016018, 0x0, 0x18}, 0x2624542108?, 0x0, 0x0, 0x7f262454d0f8?)
	/usr/local/go-faketime/src/strconv/ftoa.go:149 +0x41c
strconv.FormatFloat(0x405058?, 0x70?, 0x0, 0x60?)
	/usr/local/go-faketime/src/strconv/ftoa.go:48 +0x74
main.main()
	/tmp/sandbox175921334/prog.go:11 +0x2e

Program exited.

Found by https://github.com/catenacyber/ngolo-fuzzing on oss-fuzz
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=46427

@catenacyber
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@catenacyber catenacyber commented Apr 6, 2022

The one-liner reproducer is strconv.FormatFloat(6.013470016999068e-154, byte(0x0), int(0), int(64))

@ianlancetaylor ianlancetaylor added the NeedsInvestigation label Apr 6, 2022
@ianlancetaylor ianlancetaylor added this to the Go1.19 milestone Apr 6, 2022
@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Apr 6, 2022

@catenacyber
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@catenacyber catenacyber commented Apr 29, 2022

friendly ping @remyoudompheng What is coming for this issue ?

@remyoudompheng
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@remyoudompheng remyoudompheng commented Apr 29, 2022

Interestingly there is no issue with valid uses of the package as show by this example:

package main

import (
      "strconv"
)

func main() {
      x := 6.013470016999068e-154
      println(strconv.FormatFloat(x, 'f', 0, 64))
      println(strconv.FormatFloat(x, 'g', 0, 64))
      println(strconv.FormatFloat(x, 'e', 0, 64))
      println(strconv.FormatFloat(x, 'x', 0, 64))
}

The issue was already present in Go 1.15 with the following panic message:
panic: strconv: internal error: extFloat.FixedDecimal called with n == 0

The same message exists in Go 1.1 and probably even before (I am not able to run Go 1.0).
It seems the expected output is "%" + string(fmt)

@gopherbot
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@gopherbot gopherbot commented Apr 29, 2022

Change https://go.dev/cl/402817 mentions this issue: strconv: avoid Panic on invalid call to FormatFloat

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