Use skeema/knownhosts, not x/crypto/ssh/knownhosts

Package [golang.org/x/crypto/ssh/knownhosts](https://pkg.go.dev/golang.org/x/crypto/ssh/knownhosts)
has an issue when an SSH server has many public keys (i.e. supports multiple crypto algorithms).

For instance, if the local `known_hosts` file entries don't match the first SSH server key but match
other keys of the SSH server, the handshake fails with a key mismatch error.

See golang/go#29286 and containers/podman#23575.

Package [github.com/skeema/knownhosts](https://github.com/skeema/knownhosts) is a wrapper of
`x/crypto/ssh/knownhosts` that addresses this issue.

This commit replaces the usage of `x/crypto/ssh/knownhosts` in containers/common with
`github.com/skeema/knownhosts`.

Signed-off-by: Mario Loriedo <[email protected]>

go.mod

@@ -39,6 +39,7 @@ require (
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2
 	github.com/seccomp/libseccomp-golang v0.10.0
 	github.com/sirupsen/logrus v1.9.3
+	github.com/skeema/knownhosts v1.3.0
 	github.com/spf13/cobra v1.8.1
 	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.9.0

go.sum

@@ -300,6 +300,8 @@ github.com/sigstore/sigstore v1.8.4 h1:g4ICNpiENFnWxjmBzBDWUn62rNFeny/P77HUC8da3
 github.com/sigstore/sigstore v1.8.4/go.mod h1:1jIKtkTFEeISen7en+ZPWdDHazqhxco/+v9CNjc7oNg=
 github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
 github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
+github.com/skeema/knownhosts v1.3.0 h1:AM+y0rI04VksttfwjkSTNQorvGqmwATnvnAHpSgc0LY=
+github.com/skeema/knownhosts v1.3.0/go.mod h1:sPINvnADmT/qYH1kfv+ePMmOBTH6Tbl7b5LvTDjFK7M=
 github.com/spf13/cobra v1.8.1 h1:e5/vxKd/rZsfSJMUX1agtjeTDf+qv1/JdBF8gg5k9ZM=
 github.com/spf13/cobra v1.8.1/go.mod h1:wHxEcudfqmLYa8iTfL+OuZPbBZkmvliBWKIezN3kD9Y=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=

pkg/ssh/connection_golang.go

@@ -16,14 +16,20 @@ import (
 	"strings"
 	"time"
 
+	// We are using skeema/knownhosts rather than
+	// golang.org/x/crypto/ssh/knownhosts because the
+	// latter has an issue when the first key returned
+	// by the server doesn't match the one in known_hosts:
+	// https://github.com/golang/go/issues/29286
+	// https://github.com/containers/podman/issues/23575
 	"github.com/containers/common/pkg/config"
 	"github.com/containers/storage/pkg/fileutils"
 	"github.com/containers/storage/pkg/homedir"
 	"github.com/pkg/sftp"
 	"github.com/sirupsen/logrus"
+	"github.com/skeema/knownhosts"
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/crypto/ssh/agent"
-	"golang.org/x/crypto/ssh/knownhosts"
 	"golang.org/x/exp/maps"
 )
 
@@ -301,46 +307,44 @@ func ValidateAndConfigure(uri *url.URL, iden string, insecureIsMachineConnection
 		return nil, err
 	}
 
+	keyFilePath := filepath.Join(homedir.Get(), ".ssh", "known_hosts")
+	known, err := knownhosts.NewDB(keyFilePath)
+	if err != nil {
+		if !errors.Is(err, os.ErrNotExist) {
+			return nil, err
+		}
+		keyDir := path.Dir(keyFilePath)
+		if err := fileutils.Exists(keyDir); errors.Is(err, os.ErrNotExist) {
+			if err := os.Mkdir(keyDir, 0o700); err != nil {
+				return nil, err
+			}
+		}
+		k, err := os.OpenFile(keyFilePath, os.O_RDWR|os.O_CREATE, 0o600)
+		if err != nil {
+			return nil, err
+		}
+		k.Close()
+		known, err = knownhosts.NewDB(keyFilePath)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	var callback ssh.HostKeyCallback
 	if insecureIsMachineConnection {
 		callback = ssh.InsecureIgnoreHostKey()
 	} else {
 		callback = ssh.HostKeyCallback(func(host string, remote net.Addr, pubKey ssh.PublicKey) error {
-			keyFilePath := filepath.Join(homedir.Get(), ".ssh", "known_hosts")
-			known, err := knownhosts.New(keyFilePath)
-			if err != nil {
-				if !errors.Is(err, os.ErrNotExist) {
-					return err
-				}
-				keyDir := path.Dir(keyFilePath)
-				if err := fileutils.Exists(keyDir); errors.Is(err, os.ErrNotExist) {
-					if err := os.Mkdir(keyDir, 0o700); err != nil {
-						return err
-					}
-				}
-				k, err := os.OpenFile(keyFilePath, os.O_RDWR|os.O_CREATE, 0o600)
-				if err != nil {
-					return err
-				}
-				k.Close()
-				known, err = knownhosts.New(keyFilePath)
-				if err != nil {
-					return err
-				}
-			}
 			// we need to check if there is an error from reading known hosts for this public key and if there is an error, what is it, and why is it happening?
 			// if it is a key mismatch we want to error since we know the host using another key
 			// however, if it is a general error not because of a known key, we want to add our key to the known_hosts file
-			hErr := known(host, remote, pubKey)
-			var keyErr *knownhosts.KeyError
-			// if keyErr.Want is not empty, we are receiving a different key meaning the host is known but we are using the wrong key
-			as := errors.As(hErr, &keyErr)
+			hErr := known.HostKeyCallback()(host, remote, pubKey)
 			switch {
-			case as && len(keyErr.Want) > 0:
+			case knownhosts.IsHostKeyChanged(hErr):
 				logrus.Warnf("ssh host key mismatch for host %s, got key %s of type %s", host, ssh.FingerprintSHA256(pubKey), pubKey.Type())
-				return keyErr
+				return hErr
 			// if keyErr.Want is empty that just means we do not know this host yet, add it.
-			case as && len(keyErr.Want) == 0:
+			case knownhosts.IsHostUnknown(hErr):
 				// write to known_hosts
 				err := addKnownHostsEntry(host, pubKey)
 				if err != nil {
@@ -358,10 +362,11 @@ func ValidateAndConfigure(uri *url.URL, iden string, insecureIsMachineConnection
 	}
 
 	cfg := &ssh.ClientConfig{
-		User:            uri.User.Username(),
-		Auth:            authMethods,
-		HostKeyCallback: callback,
-		Timeout:         tick,
+		User:              uri.User.Username(),
+		Auth:              authMethods,
+		HostKeyCallback:   callback,
+		Timeout:           tick,
+		HostKeyAlgorithms: known.HostKeyAlgorithms(uri.Host),
 	}
 	return cfg, nil
 }