x/crypto/ssh: Corrupting a byte of a clients private key results in panic, rather than authorization failure

[elansys-kc]

What version of Go are you using (go version)?

go version go1.15.3 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/kc/.cache/go-build"
GOENV="/home/kc/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/kc/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/kc/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go-1.15"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.15/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="0"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build800146455=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Corrupted a byte in the read key, expecting an authorization failure.

func SSHBug() error {

	keyFile := "/home/kc/.ssh/test_ecdsa"
	key, err := ioutil.ReadFile(keyFile)
	if err != nil {
		log.Fatalf("unable to read private key: %v", err)
	}
	log.Print("Key Size ", len(key))
	key[200] = 0x0e
	signer, err := ssh.ParsePrivateKey(key)
	cred := ssh.PublicKeys(signer)

	config := &ssh.ClientConfig{
		User: "testSSH",
		Auth: []ssh.AuthMethod{
			cred,
		},
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
	}

	conn, err := ssh.Dial("tcp", "10.192.170.1:443", config)
	if err != nil {
		log.Print(err)
		return err
	}
	defer conn.Close()
	return err
}

What did you expect to see?

Failed authorization like when using an uncorrupted but unauthorized key

What did you see instead?

elansftp.go:162: Key Size 756
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x57b435]

goroutine 1 [running]:
golang.org/x/crypto/ssh.publicKeyCallback.auth(0xc00009cb20, 0xc0000186e0, 0x20, 0x20, 0x5f0da6, 0x7, 0x62af20, 0xc000066000, 0x6290e0, 0xc000086540, ...)
/home/kc/go/src/golang.org/x/crypto/ssh/client_auth.go:204 +0xd5
golang.org/x/crypto/ssh.(*connection).clientAuthenticate(0xc000060080, 0xc00005c000, 0x0, 0xa)
/home/kc/go/src/golang.org/x/crypto/ssh/client_auth.go:44 +0x343
golang.org/x/crypto/ssh.(*connection).clientHandshake(0xc000060080, 0x5f2934, 0x10, 0xc00005c000, 0x0, 0x0)
/home/kc/go/src/golang.org/x/crypto/ssh/client.go:113 +0x2c5
golang.org/x/crypto/ssh.NewClientConn(0x62c5c0, 0xc00000e010, 0x5f2934, 0x10, 0xc000041e80, 0x62c5c0, 0xc00000e010, 0x0, 0x0, 0x5c8001, ...)
/home/kc/go/src/golang.org/x/crypto/ssh/client.go:83 +0xf8
golang.org/x/crypto/ssh.Dial(0x5f051c, 0x3, 0x5f2934, 0x10, 0xc000041e80, 0x629140, 0xc000084730, 0xb)
/home/kc/go/src/golang.org/x/crypto/ssh/client.go:177 +0xbb
main.SSHBug(0x0, 0x0)
/home/kc/code/Experiments/GoSSHTest/elansftp.go:175 +0x31d
main.main()
/home/kc/code/Experiments/GoSSHTest/elansftp.go:280 +0x3b

[elansys-kc]

signer is nil as I missed the error check following this line:
signer, err := ssh.ParsePrivateKey(key)

Apologies