x/crypto/bcrypt: bcrypt.expensiveBlowfishSetup changes slice's underlying array #20425
Description
Please answer these questions before submitting your issue. Thanks!
What version of Go are you using (go version)?
go version go1.8.1 openbsd/amd64
What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="openbsd"
GOOS="openbsd"
GOPATH="/home/stuart/go"
GORACE=""
GOROOT="/home/stuart/.go/1.8.1"
GOTOOLDIR="/home/stuart/.go/1.8.1/pkg/tool/openbsd_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -fmessage-length=0"
CXX="g++"
CGO_ENABLED="0"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
What did you do?
If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.
package main
import (
"log"
"golang.org/x/crypto/bcrypt"
)
const HASH = "$2a$10$LK9XRuhNxHHCvjX3tdkRKei1QiCDUKrJRhZv7WWZPuQGRUM92rOUa"
func main() {
a := []byte("passw0rd123456")
password := a[:len(a)-6]
token := a[len(a)-6:]
log.Printf("Before: A:%q T:%q P:%q", a, token, password)
if err := bcrypt.CompareHashAndPassword([]byte(HASH), password); nil != err {
log.Fatalf("Hash mismatch")
}
log.Printf("After: A:%q T:%q P:%q", a, token, password)
}Output:
2017/05/19 11:58:43 Before: A:"passw0rd123456" T:"123456" P:"passw0rd"
2017/05/19 11:58:43 After: A:"passw0rd\x0023456" T:"\x0023456" P:"passw0rd"
What did you expect to see?
I expected the value of token to be unchanged after the call to bcrypt.CompareAndHashPassword.
What did you see instead?
The first byte of token was changed. This seems to happen in the call to bcrypt.expensiveBlowfishSetup when it appends a null byte to password to be compatible with C implementations.
https://github.com/golang/crypto/blob/master/bcrypt/bcrypt.go#L216
Unfortunately this changes the slice's underlying array, which can have knock-on effects if other slices refer to the same array (as in my 2FA-derived example).