Add `NewCredentialSSHKeyFromSigner` (#706)

This change adds `NewCredentialSSHKeyFromSigner`, which allows idiomatic
use of SSH keys from Go. This also lets us spin off an SSH server in the
tests.

(cherry picked from commit abf02bc7d7)

.github/workflows/ci.yml

@@ -34,6 +34,7 @@ jobs:
         GOPATH: /home/runner/work/git2go
       run: |
         git submodule update --init
+        sudo apt-get install -y --no-install-recommends libssh2-1-dev
         make build-libgit2-static
         go get -tags static -t github.com/${{ github.repository }}/...
         go build -tags static github.com/${{ github.repository }}/...
@@ -62,6 +63,7 @@ jobs:
     - name: Build
       run: |
         git submodule update --init
+        sudo apt-get install -y --no-install-recommends libssh2-1-dev
         make build-libgit2-static
     - name: Test
       run:  make TEST_ARGS=-test.v test-static
@@ -84,6 +86,7 @@ jobs:
     - name: Build
       run: |
         git submodule update --init
+        sudo apt-get install -y --no-install-recommends libssh2-1-dev
         make build-libgit2-dynamic
     - name: Test
       run: make TEST_ARGS=-test.v test-dynamic
@@ -106,6 +109,7 @@ jobs:
     - name: Build libgit2
       run: |
         git submodule update --init
+        sudo apt-get install -y --no-install-recommends libssh2-1-dev
         sudo ./script/build-libgit2.sh --dynamic --system
     - name: Test
       run: make TEST_ARGS=-test.v test
@@ -128,6 +132,7 @@ jobs:
     - name: Build libgit2
       run: |
         git submodule update --init
+        sudo apt-get install -y --no-install-recommends libssh2-1-dev
         sudo ./script/build-libgit2.sh --static --system
     - name: Test
       run: go test --count=1 --tags "static,system_libgit2" ./...

.travis.yml

@@ -8,6 +8,7 @@ go:
   - tip
 
 install:
+  - sudo apt-get install -y --no-install-recommends libssh2-1-dev
   - make build-libgit2-static
   - go get --tags "static" ./...
 

credentials.go

@@ -2,9 +2,16 @@ package git
 
 /*
 #include <git2.h>
+
+void _go_git_populate_credential_ssh_custom(git_cred_ssh_custom *cred);
 */
 import "C"
-import "unsafe"
+import (
+	"crypto/rand"
+	"unsafe"
+
+	"golang.org/x/crypto/ssh"
+)
 
 type CredType uint
 
@@ -89,3 +96,61 @@ func NewCredDefault() (int, Cred) {
 	ret := C.git_cred_default_new(&cred.ptr)
 	return int(ret), cred
 }
+
+type credentialSSHCustomData struct {
+	signer ssh.Signer
+}
+
+//export credentialSSHCustomFree
+func credentialSSHCustomFree(cred *C.git_cred_ssh_custom) {
+	if cred == nil {
+		return
+	}
+
+	C.free(unsafe.Pointer(cred.username))
+	C.free(unsafe.Pointer(cred.publickey))
+	pointerHandles.Untrack(cred.payload)
+	C.free(unsafe.Pointer(cred))
+}
+
+//export credentialSSHSignCallback
+func credentialSSHSignCallback(
+	errorMessage **C.char,
+	sig **C.uchar,
+	sig_len *C.size_t,
+	data *C.uchar,
+	data_len C.size_t,
+	handle unsafe.Pointer,
+) C.int {
+	signer := pointerHandles.Get(handle).(*credentialSSHCustomData).signer
+	signature, err := signer.Sign(rand.Reader, C.GoBytes(unsafe.Pointer(data), C.int(data_len)))
+	if err != nil {
+		return setCallbackError(errorMessage, err)
+	}
+	*sig = (*C.uchar)(C.CBytes(signature.Blob))
+	*sig_len = C.size_t(len(signature.Blob))
+	return C.int(ErrorCodeOK)
+}
+
+// NewCredentialSSHKeyFromSigner creates new SSH credentials using the provided signer.
+func NewCredentialSSHKeyFromSigner(username string, signer ssh.Signer) (*Cred, error) {
+	publicKey := signer.PublicKey().Marshal()
+
+	ccred := (*C.git_cred_ssh_custom)(C.calloc(1, C.size_t(unsafe.Sizeof(C.git_cred_ssh_custom{}))))
+	ccred.parent.credtype = C.GIT_CREDTYPE_SSH_CUSTOM
+	ccred.username = C.CString(username)
+	ccred.publickey = (*C.char)(C.CBytes(publicKey))
+	ccred.publickey_len = C.size_t(len(publicKey))
+	C._go_git_populate_credential_ssh_custom(ccred)
+
+	data := credentialSSHCustomData{
+		signer: signer,
+	}
+	ccred.payload = pointerHandles.Track(&data)
+
+	cred := Cred{
+		ptr: &ccred.parent,
+	}
+
+	return &cred, nil
+}

go.mod

@@ -1,3 +1,9 @@
 module github.com/libgit2/git2go/v27
 
 go 1.13
+
+require (
+	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
+	golang.org/x/crypto v0.0.0-20201203163018-be400aefbc4c
+	golang.org/x/sys v0.0.0-20201204225414-ed752295db88 // indirect
+)

go.sum

@@ -0,0 +1,13 @@
+github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510 h1:El6M4kTTCOh6aBiKaUGG7oYTSPP8MxqL4YI3kZKwcP4=
+github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510/go.mod h1:pupxD2MaaD3pAXIBCelhxNneeOaAeabZDe5s4K6zSpQ=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20201203163018-be400aefbc4c h1:9HhBz5L/UjnK9XLtiZhYAdue5BVKep3PMmS2LuPDt8k=
+golang.org/x/crypto v0.0.0-20201203163018-be400aefbc4c/go.mod h1:jdWPYTVW3xRLrWPugEBEK3UY2ZEsg3UU495nc5E+M+I=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201204225414-ed752295db88 h1:KmZPnMocC93w341XZp26yTJg8Za7lhb2KhkYmixoeso=
+golang.org/x/sys v0.0.0-20201204225414-ed752295db88/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/term v0.0.0-20201117132131-f5c789dd3221 h1:/ZHdbVpdR/jk3g30/d4yUL0JU9kksj8+F/bnQUVLGDM=
+golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

remote_test.go

@@ -1,8 +1,21 @@
 package git
 
 import (
+	"bytes"
+	"crypto/rand"
+	"crypto/rsa"
 	"fmt"
+	"io"
+	"net"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
 	"testing"
+	"time"
+
+	"github.com/google/shlex"
+	"golang.org/x/crypto/ssh"
 )
 
 func TestListRemotes(t *testing.T) {
@@ -184,3 +197,269 @@ func TestRemotePrune(t *testing.T) {
 		t.Fatal("Expected error getting a pruned reference")
 	}
 }
+
+func newChannelPipe(t *testing.T, w io.Writer, wg *sync.WaitGroup) (*os.File, error) {
+	pr, pw, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+
+	wg.Add(1)
+	go func() {
+		_, err := io.Copy(w, pr)
+		if err != nil && err != io.EOF {
+			t.Logf("Failed to copy: %v", err)
+		}
+		wg.Done()
+	}()
+
+	return pw, nil
+}
+
+func startSSHServer(t *testing.T, hostKey ssh.Signer, authorizedKeys []ssh.PublicKey) net.Listener {
+	t.Helper()
+
+	marshaledAuthorizedKeys := make([][]byte, len(authorizedKeys))
+	for i, authorizedKey := range authorizedKeys {
+		marshaledAuthorizedKeys[i] = authorizedKey.Marshal()
+	}
+
+	config := &ssh.ServerConfig{
+		PublicKeyCallback: func(c ssh.ConnMetadata, pubKey ssh.PublicKey) (*ssh.Permissions, error) {
+			marshaledPubKey := pubKey.Marshal()
+			for _, marshaledAuthorizedKey := range marshaledAuthorizedKeys {
+				if bytes.Equal(marshaledPubKey, marshaledAuthorizedKey) {
+					return &ssh.Permissions{
+						// Record the public key used for authentication.
+						Extensions: map[string]string{
+							"pubkey-fp": ssh.FingerprintSHA256(pubKey),
+						},
+					}, nil
+				}
+			}
+			t.Logf("unknown public key for %q:\n\t%+v\n\t%+v\n", c.User(), pubKey.Marshal(), authorizedKeys)
+			return nil, fmt.Errorf("unknown public key for %q", c.User())
+		},
+	}
+	config.AddHostKey(hostKey)
+
+	listener, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		t.Fatalf("Failed to listen for connection: %v", err)
+	}
+
+	go func() {
+		nConn, err := listener.Accept()
+		if err != nil {
+			if strings.Contains(err.Error(), "use of closed network connection") {
+				return
+			}
+			t.Logf("Failed to accept incoming connection: %v", err)
+			return
+		}
+		defer nConn.Close()
+
+		conn, chans, reqs, err := ssh.NewServerConn(nConn, config)
+		if err != nil {
+			t.Logf("failed to handshake: %+v, %+v", conn, err)
+			return
+		}
+
+		// The incoming Request channel must be serviced.
+		go func() {
+			for newRequest := range reqs {
+				t.Logf("new request %v", newRequest)
+			}
+		}()
+
+		// Service only the first channel request
+		newChannel := <-chans
+		defer func() {
+			for newChannel := range chans {
+				t.Logf("new channel %v", newChannel)
+				newChannel.Reject(ssh.UnknownChannelType, "server closing")
+			}
+		}()
+
+		// Channels have a type, depending on the application level
+		// protocol intended. In the case of a shell, the type is
+		// "session" and ServerShell may be used to present a simple
+		// terminal interface.
+		if newChannel.ChannelType() != "session" {
+			newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
+			return
+		}
+		channel, requests, err := newChannel.Accept()
+		if err != nil {
+			t.Logf("Could not accept channel: %v", err)
+			return
+		}
+		defer channel.Close()
+
+		// Sessions have out-of-band requests such as "shell",
+		// "pty-req" and "env".  Here we handle only the
+		// "exec" request.
+		req := <-requests
+		if req.Type != "exec" {
+			req.Reply(false, nil)
+			return
+		}
+		// RFC 4254 Section 6.5.
+		var payload struct {
+			Command string
+		}
+		if err := ssh.Unmarshal(req.Payload, &payload); err != nil {
+			t.Logf("invalid payload on channel %v: %v", channel, err)
+			req.Reply(false, nil)
+			return
+		}
+		args, err := shlex.Split(payload.Command)
+		if err != nil {
+			t.Logf("invalid command on channel %v: %v", channel, err)
+			req.Reply(false, nil)
+			return
+		}
+		if len(args) < 2 || (args[0] != "git-upload-pack" && args[0] != "git-receive-pack") {
+			t.Logf("invalid command (%v) on channel %v: %v", args, channel, err)
+			req.Reply(false, nil)
+			return
+		}
+		req.Reply(true, nil)
+
+		go func(in <-chan *ssh.Request) {
+			for req := range in {
+				t.Logf("draining request %v", req)
+			}
+		}(requests)
+
+		// The first parameter is the (absolute) path of the repository.
+		args[1] = "./testdata" + args[1]
+
+		cmd := exec.Command(args[0], args[1:]...)
+		cmd.Stdin = channel
+		var wg sync.WaitGroup
+		stdoutPipe, err := newChannelPipe(t, channel, &wg)
+		if err != nil {
+			t.Logf("Failed to create stdout pipe: %v", err)
+			return
+		}
+		cmd.Stdout = stdoutPipe
+		stderrPipe, err := newChannelPipe(t, channel.Stderr(), &wg)
+		if err != nil {
+			t.Logf("Failed to create stderr pipe: %v", err)
+			return
+		}
+		cmd.Stderr = stderrPipe
+
+		go func() {
+			wg.Wait()
+			channel.CloseWrite()
+		}()
+
+		err = cmd.Start()
+		if err != nil {
+			t.Logf("Failed to start %v: %v", args, err)
+			return
+		}
+
+		// Once the process has started, we need to close the write end of the
+		// pipes from this process so that we can know when the child has done
+		// writing to it.
+		stdoutPipe.Close()
+		stderrPipe.Close()
+
+		timer := time.AfterFunc(5*time.Second, func() {
+			t.Log("process timed out, terminating")
+			cmd.Process.Kill()
+		})
+		defer timer.Stop()
+
+		err = cmd.Wait()
+		if err != nil {
+			t.Logf("Failed to run %v: %v", args, err)
+			return
+		}
+	}()
+	return listener
+}
+
+func TestRemoteSSH(t *testing.T) {
+	t.Parallel()
+	pubKeyUsername := "testuser"
+
+	hostPrivKey, err := rsa.GenerateKey(rand.Reader, 512)
+	if err != nil {
+		t.Fatalf("Failed to generate the host RSA private key: %v", err)
+	}
+	hostSigner, err := ssh.NewSignerFromKey(hostPrivKey)
+	if err != nil {
+		t.Fatalf("Failed to generate SSH hostSigner: %v", err)
+	}
+
+	privKey, err := rsa.GenerateKey(rand.Reader, 512)
+	if err != nil {
+		t.Fatalf("Failed to generate the user RSA private key: %v", err)
+	}
+	signer, err := ssh.NewSignerFromKey(privKey)
+	if err != nil {
+		t.Fatalf("Failed to generate SSH signer: %v", err)
+	}
+	// This is in the format "xx:xx:xx:...", so we remove the colons so that it
+	// matches the fmt.Sprintf() below.
+	// Note that not all libssh2 implementations support the SHA256 fingerprint,
+	// so we use MD5 here for testing.
+	publicKeyFingerprint := strings.Replace(ssh.FingerprintLegacyMD5(hostSigner.PublicKey()), ":", "", -1)
+
+	listener := startSSHServer(t, hostSigner, []ssh.PublicKey{signer.PublicKey()})
+	defer listener.Close()
+
+	repo := createTestRepo(t)
+	defer cleanupTestRepo(t, repo)
+
+	certificateCheckCallbackCalled := false
+	fetchOpts := FetchOptions{
+		RemoteCallbacks: RemoteCallbacks{
+			CertificateCheckCallback: func(cert *Certificate, valid bool, hostname string) ErrorCode {
+				hostkeyFingerprint := fmt.Sprintf("%x", cert.Hostkey.HashMD5[:])
+				if hostkeyFingerprint != publicKeyFingerprint {
+					t.Logf("server hostkey %q, want %q", hostkeyFingerprint, publicKeyFingerprint)
+					return ErrorCodeAuth
+				}
+				certificateCheckCallbackCalled = true
+				return ErrorCodeOK
+			},
+			CredentialsCallback: func(url, username string, allowedTypes CredType) (ErrorCode, *Cred) {
+				if allowedTypes&(CredTypeSshKey|CredTypeSshCustom) != 0 {
+					cred, err := NewCredentialSSHKeyFromSigner(pubKeyUsername, signer)
+					if err != nil {
+						t.Logf("failed to create credentials: %v", err)
+						return ErrorCodeAuth, nil
+					}
+					return ErrorCodeOK, cred
+				}
+				t.Logf("unknown credential type %+v", allowedTypes)
+				return ErrorCodeAuth, nil
+			},
+		},
+	}
+
+	remote, err := repo.Remotes.Create(
+		"origin",
+		fmt.Sprintf("ssh://%s@%s/TestGitRepository", pubKeyUsername, listener.Addr().String()),
+	)
+	checkFatal(t, err)
+	defer remote.Free()
+
+	err = remote.Fetch(nil, &fetchOpts, "")
+	checkFatal(t, err)
+	if !certificateCheckCallbackCalled {
+		t.Fatalf("CertificateCheckCallback was not called")
+	}
+
+	heads, err := remote.Ls()
+	checkFatal(t, err)
+
+	if len(heads) == 0 {
+		t.Error("Expected remote heads")
+	}
+}

script/build-libgit2.sh

@@ -62,11 +62,11 @@ cmake -DTHREADSAFE=ON \
       -DCMAKE_BUILD_TYPE="RelWithDebInfo" \
       -DCMAKE_INSTALL_PREFIX="${BUILD_INSTALL_PREFIX}" \
       -DDEPRECATE_HARD=ON \
-      "${VENDORED_PATH}" &&
+      "${VENDORED_PATH}"
 
-if which gmake nproc >/dev/null && [ -f Makefile ]; then
+if which make nproc >/dev/null && [ -f Makefile ]; then
-	# Make the build parallel if gmake is available and cmake used Makefiles.
+	# Make the build parallel if make is available and cmake used Makefiles.
-	exec gmake "-j$(nproc --all)" install
+	exec make "-j$(nproc --all)" install
+else
+	exec cmake --build . --target install
 fi
-
-exec cmake --build . --target install

testdata/TestGitRepository.git/HEAD

@@ -0,0 +1 @@
+ref: refs/heads/master

testdata/TestGitRepository.git/config

@@ -0,0 +1,6 @@
+[core]
+	repositoryformatversion = 0
+	filemode = true
+	bare = true
+[remote "origin"]
+	url = https://github.com/libgit2/TestGitRepository

testdata/TestGitRepository.git/description

@@ -0,0 +1 @@
+Unnamed repository; edit this file 'description' to name the repository.

testdata/TestGitRepository.git/info/exclude

@@ -0,0 +1,6 @@
+# git ls-files --others --exclude-from=.git/info/exclude
+# Lines that start with '#' are comments.
+# For a project mostly in C, the following would be a good set of
+# exclude patterns (uncomment them if you want to use them):
+# *.[oa]
+# *~

testdata/TestGitRepository.git/info/refs

@@ -0,0 +1,8 @@
+0966a434eb1a025db6b71485ab63a3bfbea520b6	refs/heads/first-merge
+49322bb17d3acc9146f98c97d078513228bbf3c0	refs/heads/master
+42e4e7c5e507e113ebbb7801b16b52cf867b7ce1	refs/heads/no-parent
+d96c4e80345534eccee5ac7b07fc7603b56124cb	refs/tags/annotated_tag
+c070ad8c08840c8116da865b2d65593a6bb9cd2a	refs/tags/annotated_tag^{}
+55a1a760df4b86a02094a904dfa511deb5655905	refs/tags/blob
+8f50ba15d49353813cc6e20298002c0d17b0a9ee	refs/tags/commit_tree
+6e0c7bdb9b4ed93212491ee778ca1c65047cab4e	refs/tags/nearly-dangling

testdata/TestGitRepository.git/objects/info/packs

@@ -0,0 +1,2 @@
+P pack-ccace4e169a0858c13d9ae781a91d76fc33769b8.pack
+

testdata/TestGitRepository.git/packed-refs

@@ -0,0 +1,9 @@
+# pack-refs with: peeled fully-peeled sorted 
+0966a434eb1a025db6b71485ab63a3bfbea520b6 refs/heads/first-merge
+49322bb17d3acc9146f98c97d078513228bbf3c0 refs/heads/master
+42e4e7c5e507e113ebbb7801b16b52cf867b7ce1 refs/heads/no-parent
+d96c4e80345534eccee5ac7b07fc7603b56124cb refs/tags/annotated_tag
+^c070ad8c08840c8116da865b2d65593a6bb9cd2a
+55a1a760df4b86a02094a904dfa511deb5655905 refs/tags/blob
+8f50ba15d49353813cc6e20298002c0d17b0a9ee refs/tags/commit_tree
+6e0c7bdb9b4ed93212491ee778ca1c65047cab4e refs/tags/nearly-dangling

testdata/TestGitRepository.git/refs/heads/master

@@ -0,0 +1 @@
+49322bb17d3acc9146f98c97d078513228bbf3c0

wrapper.c

@@ -403,6 +403,29 @@ void _go_git_writestream_free(git_writestream *stream)
 	stream->free(stream);
 }
 
+static int credential_ssh_sign_callback(
+		LIBSSH2_SESSION *session,
+		unsigned char **sig, size_t *sig_len,
+		const unsigned char *data, size_t data_len,
+		void **abstract)
+{
+	char *error_message = NULL;
+	const int ret = credentialSSHSignCallback(
+			&error_message,
+			sig,
+			sig_len,
+			(unsigned char *)data,
+			data_len,
+			(void *)*(uintptr_t *)abstract);
+	return set_callback_error(error_message, ret);
+}
+
+void _go_git_populate_credential_ssh_custom(git_cred_ssh_custom *cred)
+{
+	cred->parent.free = (void (*)(git_cred *))credentialSSHCustomFree;
+	cred->sign_callback = credential_ssh_sign_callback;
+}
+
 int _go_git_odb_write_pack(git_odb_writepack **out, git_odb *db, void *progress_payload)
 {
 	return git_odb_write_pack(out, db, transfer_progress_callback, progress_payload);