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plumbing: transport/ssh, auto-populate ClientConfig.HostKeyAlgorithms. …
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…Fixes go-git#411

This commit adjusts the transport/ssh logic in command.connect(), so that it
now auto-populates ssh.ClientConfig.HostKeyAlgorithms. The algorithms are
chosen based on the known host keys for the target host, as obtained from the
known_hosts file.

In order to look-up the algorithms from the known_hosts file, external module
github.com/skeema/knownhosts is used. This package is just a thin wrapper
around golang.org/x/crypto/ssh/knownhosts, adding an extra mechanism to query
the known_hosts keys, implemented in a way which avoids duplication of any
golang.org/x/crypto/ssh/knownhosts logic.

Because HostKeyAlgorithms vary by target host, some related logic for setting
HostKeyCallback has been moved out of the various AuthMethod implementations.
This was necessary because the old HostKeyCallbackHelper is not host-specific.
Since known_hosts handling isn't really tied to AuthMethod anyway, it seems
reasonable to separate these. Previously-exported types/methods remain in
place for backwards compat, but some of them are now unused.

For testing approach, see pull request. Issue go-git#411 can only be reproduced
via end-to-end / integration testing, since it requires actually launching
an SSH connection, in order to see the key mismatch error triggered from
golang/go#29286 as the root cause.
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@evanelias @rohankmr414
evanelias authored and rohankmr414 committed Oct 12, 2022
1 parent 7a745b8 commit b07b1dd
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Showing 4 changed files with 55 additions and 25 deletions.
7 changes: 4 additions & 3 deletions go.mod
View file
Expand Up @@ -17,12 +17,13 @@ require (
github.com/jessevdk/go-flags v1.5.0
github.com/kevinburke/ssh_config v0.0.0-20201106050909-4977a11b4351
github.com/sergi/go-diff v1.1.0
github.com/skeema/knownhosts v1.1.0
github.com/whilp/git-urls v1.0.0
github.com/xanzy/ssh-agent v0.3.1
golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97
golang.org/x/net v0.0.0-20210326060303-6b1517762897
golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e
golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2
golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c
golang.org/x/text v0.3.3
golang.org/x/text v0.3.6
gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c
gopkg.in/warnings.v0 v0.1.2 // indirect
)
Expand Down
14 changes: 9 additions & 5 deletions go.sum
View file
Expand Up @@ -51,6 +51,8 @@ github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZN
github.com/sergi/go-diff v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
github.com/sergi/go-diff v1.1.0/go.mod h1:STckp+ISIX8hZLjrqAeVduY0gWCT9IjLuqbuNXdaHfM=
github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
github.com/skeema/knownhosts v1.1.0 h1:Wvr9V0MxhjRbl3f9nMnKnFfiWTJmtECJ9Njkea3ysW0=
github.com/skeema/knownhosts v1.1.0/go.mod h1:sKFq3RD6/TKZkSWn8boUbDC7Qkgcv+8XXijpFO6roag=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
Expand All @@ -61,24 +63,26 @@ github.com/whilp/git-urls v1.0.0/go.mod h1:J16SAmobsqc3Qcy98brfl5f5+e0clUvg1krgw
github.com/xanzy/ssh-agent v0.3.1 h1:AmzO1SSWxw73zxFZPRwaMN1MohDw8UyHnmuxyceTEGo=
github.com/xanzy/ssh-agent v0.3.1/go.mod h1:QIE4lCeL7nkC25x+yA3LBIYfwCc1TFziCtG7cBAac6w=
golang.org/x/crypto v0.0.0-20210322153248-0c34fe9e7dc2/go.mod h1:T9bdIzuCu7OtxOm1hfPfRQxPLYneinmdGuTeoZ9dtd4=
golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97 h1:/UOmuWzQfxxo9UtlXMwuQU8CMgg1eZXqTRwkSQJWKOI=
golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e h1:T8NU3HyQ8ClP4SEE+KbFlg6n0NhuTsN4MyznaarGsZM=
golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
golang.org/x/net v0.0.0-20210326060303-6b1517762897 h1:KrsHThm5nFk34YtATK1LsThyGhGbGe1olrte/HInHvs=
golang.org/x/net v0.0.0-20210326060303-6b1517762897/go.mod h1:uSPa2vr4CLtc/ILN5odXGNXS6mhrKVzTaCXzk9m6W3k=
golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2 h1:CIJ76btIcR3eFI5EgSo6k1qKw9KJexJuRLI9G7Hp5wE=
golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20200302150141-5c8b2ff67527/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210124154548-22da62e12c0c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210320140829-1e4c9ba3b0c4/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210324051608-47abb6519492/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c h1:F1jZWGFhYfh0Ci55sIpILtKKK8p3i2/krTr0H1rg74I=
golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1 h1:v+OssWQX+hTHEmOBgwxdZxK4zHq3yOs8F9J7mk0PY8E=
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.6 h1:aRYxNxv6iGQlyVaZmk6ZgYEDa+Jg18DxebPSrd6bg1M=
golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
Expand Down
35 changes: 19 additions & 16 deletions plumbing/transport/ssh/auth_method.go
View file
Expand Up @@ -10,9 +10,9 @@ import (

"github.com/go-git/go-git/v5/plumbing/transport"

"github.com/skeema/knownhosts"
sshagent "github.com/xanzy/ssh-agent"
"golang.org/x/crypto/ssh"
"golang.org/x/crypto/ssh/knownhosts"
)

const DefaultUsername = "git"
Expand Down Expand Up @@ -43,7 +43,6 @@ const (
type KeyboardInteractive struct {
User string
Challenge ssh.KeyboardInteractiveChallenge
HostKeyCallbackHelper
}

func (a *KeyboardInteractive) Name() string {
Expand All @@ -55,19 +54,18 @@ func (a *KeyboardInteractive) String() string {
}

func (a *KeyboardInteractive) ClientConfig() (*ssh.ClientConfig, error) {
return a.SetHostKeyCallback(&ssh.ClientConfig{
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{
a.Challenge,
},
})
}, nil
}

// Password implements AuthMethod by using the given password.
type Password struct {
User string
Password string
HostKeyCallbackHelper
}

func (a *Password) Name() string {
Expand All @@ -79,18 +77,17 @@ func (a *Password) String() string {
}

func (a *Password) ClientConfig() (*ssh.ClientConfig, error) {
return a.SetHostKeyCallback(&ssh.ClientConfig{
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.Password(a.Password)},
})
}, nil
}

// PasswordCallback implements AuthMethod by using a callback
// to fetch the password.
type PasswordCallback struct {
User string
Callback func() (pass string, err error)
HostKeyCallbackHelper
}

func (a *PasswordCallback) Name() string {
Expand All @@ -102,17 +99,16 @@ func (a *PasswordCallback) String() string {
}

func (a *PasswordCallback) ClientConfig() (*ssh.ClientConfig, error) {
return a.SetHostKeyCallback(&ssh.ClientConfig{
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)},
})
}, nil
}

// PublicKeys implements AuthMethod by using the given key pairs.
type PublicKeys struct {
User string
Signer ssh.Signer
HostKeyCallbackHelper
}

// NewPublicKeys returns a PublicKeys from a PEM encoded private key. An
Expand Down Expand Up @@ -151,10 +147,10 @@ func (a *PublicKeys) String() string {
}

func (a *PublicKeys) ClientConfig() (*ssh.ClientConfig, error) {
return a.SetHostKeyCallback(&ssh.ClientConfig{
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.PublicKeys(a.Signer)},
})
}, nil
}

func username() (string, error) {
Expand All @@ -177,7 +173,6 @@ func username() (string, error) {
type PublicKeysCallback struct {
User string
Callback func() (signers []ssh.Signer, err error)
HostKeyCallbackHelper
}

// NewSSHAgentAuth returns a PublicKeysCallback based on a SSH agent, it opens
Expand Down Expand Up @@ -212,10 +207,10 @@ func (a *PublicKeysCallback) String() string {
}

func (a *PublicKeysCallback) ClientConfig() (*ssh.ClientConfig, error) {
return a.SetHostKeyCallback(&ssh.ClientConfig{
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)},
})
}, nil
}

// NewKnownHostsCallback returns ssh.HostKeyCallback based on a file based on a
Expand All @@ -231,6 +226,11 @@ func (a *PublicKeysCallback) ClientConfig() (*ssh.ClientConfig, error) {
// ~/.ssh/known_hosts
// /etc/ssh/ssh_known_hosts
func NewKnownHostsCallback(files ...string) (ssh.HostKeyCallback, error) {
kh, err := newKnownHosts(files...)
return ssh.HostKeyCallback(kh), err
}

func newKnownHosts(files ...string) (knownhosts.HostKeyCallback, error) {
var err error

if len(files) == 0 {
Expand Down Expand Up @@ -286,6 +286,9 @@ func filterKnownHostsFiles(files ...string) ([]string, error) {

// HostKeyCallbackHelper is a helper that provides common functionality to
// configure HostKeyCallback into a ssh.ClientConfig.
// Deprecated in favor of SetConfigHostKeyFields (see common.go) which provides
// a mechanism for also setting ClientConfig.HostKeyAlgorithms for a specific
// host.
type HostKeyCallbackHelper struct {
// HostKeyCallback is the function type used for verifying server keys.
// If nil default callback will be create using NewKnownHostsCallback
Expand Down
24 changes: 23 additions & 1 deletion plumbing/transport/ssh/common.go
View file
Expand Up @@ -121,10 +121,15 @@ func (c *command) connect() error {
if err != nil {
return err
}
hostWithPort := c.getHostWithPort()
config, err = SetConfigHostKeyFields(config, hostWithPort)
if err != nil {
return err
}

overrideConfig(c.config, config)

c.client, err = dial("tcp", c.getHostWithPort(), config)
c.client, err = dial("tcp", hostWithPort, config)
if err != nil {
return err
}
Expand Down Expand Up @@ -162,6 +167,23 @@ func dial(network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
return ssh.NewClient(c, chans, reqs), nil
}

// SetConfigHostKeyFields sets cfg.HostKeyCallback and cfg.HostKeyAlgorithms
// based on OpenSSH known_hosts. cfg is modified in-place. hostWithPort must be
// supplied, since the algorithms will be set based on the known host keys for
// that specific host. Otherwise, golang.org/x/crypto/ssh can return an error
// upon connecting to a host whose *first* key is not known, even though other
// keys (of different types) are known and match properly.
// For background see https://github.com/go-git/go-git/issues/411 as well as
// https://github.com/golang/go/issues/29286 for root cause.
func SetConfigHostKeyFields(cfg *ssh.ClientConfig, hostWithPort string) (*ssh.ClientConfig, error) {
kh, err := newKnownHosts()
if err == nil {
cfg.HostKeyCallback = kh.HostKeyCallback()
cfg.HostKeyAlgorithms = kh.HostKeyAlgorithms(hostWithPort)
}
return cfg, err
}

func (c *command) getHostWithPort() string {
if addr, found := c.doGetHostWithPortFromSSHConfig(); found {
return addr
Expand Down

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