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package server
import (
"errors"
"fmt"
iofs "io/fs"
"os"
goUser "os/user"
"path/filepath"
"github.com/mimecast/dtail/internal/config"
"github.com/mimecast/dtail/internal/io/dlog"
"github.com/mimecast/dtail/internal/io/fs"
user "github.com/mimecast/dtail/internal/user/server"
gossh "golang.org/x/crypto/ssh"
)
// NewPublicKeyCallback creates an instance-scoped SSH public key callback.
// It avoids relying on package-level mutable configuration/state.
func NewPublicKeyCallback(authKeyEnabled bool, cacheDir string,
keyStore *AuthKeyStore) func(gossh.ConnMetadata, gossh.PublicKey) (*gossh.Permissions, error) {
if keyStore == nil {
keyStore = authKeyStore
}
return func(c gossh.ConnMetadata, offeredPubKey gossh.PublicKey) (*gossh.Permissions, error) {
return publicKeyCallback(c, offeredPubKey, authKeyEnabled, cacheDir, keyStore)
}
}
func publicKeyCallback(c gossh.ConnMetadata, offeredPubKey gossh.PublicKey,
authKeyEnabled bool, cacheDir string, keyStore *AuthKeyStore) (*gossh.Permissions, error) {
user, err := user.New(c.User(), c.RemoteAddr().String(), nil)
if err != nil {
return nil, err
}
dlog.Server.Info(user, "Incoming authorization")
if authKeyEnabled {
if permissions := authKeyStorePermissions(keyStore, user.Name, offeredPubKey); permissions != nil {
dlog.Server.Info(user, "Authorized by in-memory auth key store")
return permissions, nil
}
}
authorizedKeysPath, err := authorizedKeysPathForUser(user, cacheDir)
if err != nil {
return nil, err
}
dlog.Server.Info(user, "Reading", authorizedKeysPath.Path())
authorizedKeysBytes, err := authorizedKeysPath.ReadFile()
if err != nil {
return nil, fmt.Errorf("Unable to read authorized keys file|%s|%s|%s",
authorizedKeysPath.Path(), user, err.Error())
}
return verifyAuthorizedKeys(user, authorizedKeysBytes, offeredPubKey)
}
func verifyAuthorizedKeys(user *user.User, authorizedKeysBytes []byte,
offeredPubKey gossh.PublicKey) (*gossh.Permissions, error) {
authorizedKeysMap := map[string]bool{}
for len(authorizedKeysBytes) > 0 {
authorizedPubKey, _, _, restBytes, err := gossh.ParseAuthorizedKey(authorizedKeysBytes)
if err != nil {
return nil, fmt.Errorf("unable to parse authorized keys bytes|%s|%s",
user, err.Error())
}
authorizedKeysMap[string(authorizedPubKey.Marshal())] = true
authorizedKeysBytes = restBytes
dlog.Server.Debug(user, "Authorized public key fingerprint",
gossh.FingerprintSHA256(authorizedPubKey))
}
dlog.Server.Debug(user, "Offered public key fingerprint", gossh.FingerprintSHA256(offeredPubKey))
if authorizedKeysMap[string(offeredPubKey.Marshal())] {
return permissionsFromPublicKey(offeredPubKey), nil
}
return nil, fmt.Errorf("%s|public key of user not authorized", user)
}
func authKeyStorePermissions(keyStore *AuthKeyStore, userName string,
offeredPubKey gossh.PublicKey) *gossh.Permissions {
if keyStore == nil || !keyStore.Has(userName, offeredPubKey) {
return nil
}
return permissionsFromPublicKey(offeredPubKey)
}
func permissionsFromPublicKey(offeredPubKey gossh.PublicKey) *gossh.Permissions {
return &gossh.Permissions{
Extensions: map[string]string{"pubkey-fp": gossh.FingerprintSHA256(offeredPubKey)},
}
}
type userLookupFunc func(string) (*goUser.User, error)
func authorizedKeysPathForUser(user *user.User, cacheDir string) (fs.RootedPath, error) {
if config.Env("DTAIL_INTEGRATION_TEST_RUN_MODE") {
// In this case, we expect a pub key in the current directory.
return fs.NewRootedPath("./id_rsa.pub")
}
cwd, err := os.Getwd()
if err != nil {
return fs.RootedPath{}, err
}
return findAuthorizedKeysPath(user, cacheDir, cwd, goUser.Lookup)
}
func findAuthorizedKeysPath(user *user.User, cacheDir, cwd string,
lookupUser userLookupFunc) (fs.RootedPath, error) {
// Check for cached version in the dserver directory.
if cacheDir != "" {
cachePath := filepath.Join(cwd, cacheDir, fmt.Sprintf("%s.authorized_keys", user.Name))
rootedCachePath, err := fs.NewRootedPath(cachePath)
if err != nil {
return fs.RootedPath{}, err
}
if _, err := rootedCachePath.Stat(); err == nil {
return rootedCachePath, nil
}
}
// As the last option, check the regular SSH path.
osUser, err := lookupUser(user.Name)
if err != nil {
return fs.RootedPath{}, err
}
authorizedKeysPath := filepath.Join(osUser.HomeDir, ".ssh", "authorized_keys")
rootedAuthorizedKeysPath, err := fs.NewRootedPath(authorizedKeysPath)
if err != nil {
return fs.RootedPath{}, err
}
if _, err = rootedAuthorizedKeysPath.Stat(); err == nil {
return rootedAuthorizedKeysPath, nil
}
if !errors.Is(err, iofs.ErrNotExist) {
return fs.RootedPath{}, err
}
return fs.RootedPath{}, fmt.Errorf("unable to find any authorized keys file")
}
|
