nil pointer dereference when connecting to SSH based URLs with invalid proxy address

[anandf]

When trying to list references from a remote git repository, through a socks5 proxy, there is a nil pointer dereference operation causing the code to panic. In the below code, I am setting proxy server url as socks5://127.0.0.1:1080. If the proxy server is running, then the code behaves correctly, but if the proxy server is not running, the code panics at this line of code session, err := gitClient.NewUploadPackSession(ep, auth)

Reproducer code:

package main

import (
	"fmt"

	"github.com/go-git/go-git/v5/plumbing/transport"
	"github.com/go-git/go-git/v5/plumbing/transport/client"
	"github.com/go-git/go-git/v5/plumbing/transport/ssh"
)

func main() {
	ep, err := transport.NewEndpoint("git@github.com:anandf/openshift-gitops-microshift.git")
	if err != nil {
		fmt.Println(err)
		return
	}
	ep.Proxy = transport.ProxyOptions{URL: "socks5://127.0.0.1:1080"}
	gitClient, err := client.NewClient(ep)
	if err != nil {
		fmt.Println("Error:" + err.Error())
		return
	}
	auth, err := ssh.NewPublicKeysFromFile("git", "/home/anjoseph/.ssh/id_rsa", "")
	if err != nil {
		fmt.Println("Error:" + err.Error())
		return
	}
	session, err := gitClient.NewUploadPackSession(ep, auth)
	if err != nil {
		fmt.Println("Error:" + err.Error())
		return
	}
	ar, err := session.AdvertisedReferences()
	if err != nil {
		fmt.Println("Error:" + err.Error())
		return
	}
	allRefs, err := ar.AllReferences()
	if err != nil {
		fmt.Println("Error:" + err.Error())
		return
	}
	fmt.Println(allRefs)
	err = session.Close()
	if err != nil {
		fmt.Println("Error:" + err.Error())
		return
	}
}

[pjbgf]

@anandf thank you for reporting this. Do you mind sharing the stack trace please?

[anandf]

yes, I have the code fix as well. Will be submitting a PR.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x8cdac6]

goroutine 1 [running]:
golang.org/x/crypto/ssh.exchangeVersions({0x0, 0x0}, {0xc000205594, 0xa, 0xa})
	/home/anjoseph/go/pkg/mod/golang.org/x/crypto@v0.14.0/ssh/transport.go:302 +0x1c6
golang.org/x/crypto/ssh.(*connection).clientHandshake(0xc00023a280, {0xc000205550, 0xd}, 0xc000218340)
	/home/anjoseph/go/pkg/mod/golang.org/x/crypto@v0.14.0/ssh/client.go:100 +0x22b
golang.org/x/crypto/ssh.NewClientConn({0x0, 0x0}, {0xc000205550, 0xd}, 0xc00011fba0)
	/home/anjoseph/go/pkg/mod/golang.org/x/crypto@v0.14.0/ssh/client.go:83 +0x1fa
github.com/go-git/go-git/v5/plumbing/transport/ssh.dial({0x9acd5b, 0x3}, {0xc000205550, 0xd}, {{0x9b4675, 0x17}, {0x0, 0x0}, {0x0, 0x0}}, ...)
	/home/anjoseph/go/pkg/mod/github.com/go-git/go-git/v5@v5.10.0/plumbing/transport/ssh/common.go:197 +0xaa5
github.com/go-git/go-git/v5/plumbing/transport/ssh.(*command).connect(0xc000168730)
	/home/anjoseph/go/pkg/mod/github.com/go-git/go-git/v5@v5.10.0/plumbing/transport/ssh/common.go:143 +0x499
github.com/go-git/go-git/v5/plumbing/transport/ssh.(*runner).Command(0xc000118578, {0x9b07e2, 0xf}, 0xc000140370, {0xa09528, 0xc0001d4000})
	/home/anjoseph/go/pkg/mod/github.com/go-git/go-git/v5@v5.10.0/plumbing/transport/ssh/common.go:55 +0x176
github.com/go-git/go-git/v5/plumbing/transport/internal/common.(*client).newSession(0xc0001a0090, {0x9b07e2, 0xf}, 0xc000140370, {0xa09528, 0xc0001d4000})
	/home/anjoseph/go/pkg/mod/github.com/go-git/go-git/v5@v5.10.0/plumbing/transport/internal/common/common.go:116 +0xb0
github.com/go-git/go-git/v5/plumbing/transport/internal/common.(*client).NewUploadPackSession(0xc0001a0090, 0xc000140370, {0xa09528, 0xc0001d4000})
	/home/anjoseph/go/pkg/mod/github.com/go-git/go-git/v5@v5.10.0/plumbing/transport/internal/common/common.go:93 +0x85
main.main()
	/home/anjoseph/go/src/github.com/anandf/socks5-example/main.go:25 +0x58e