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package server
import (
"bytes"
"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"
)
type authorizedKeyParser func([]byte) (gossh.PublicKey, string, []string, []byte, error)
// NewPublicKeyCallback creates an instance-scoped SSH public key callback.
// keyStore must be non-nil; callers are responsible for constructing and
// wiring the store. There is no shared package-level fallback.
func NewPublicKeyCallback(authKeyEnabled bool, cacheDir string,
keyStore *AuthKeyStore) func(gossh.ConnMetadata, gossh.PublicKey) (*gossh.Permissions, error) {
if keyStore == nil {
panic("NewPublicKeyCallback: keyStore must not be nil")
}
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) {
return verifyAuthorizedKeysWithParser(user, authorizedKeysBytes, offeredPubKey, gossh.ParseAuthorizedKey)
}
func verifyAuthorizedKeysWithParser(user *user.User, authorizedKeysBytes []byte,
offeredPubKey gossh.PublicKey, parseAuthorizedKey authorizedKeyParser) (*gossh.Permissions, error) {
authorizedKeysMap := map[string]bool{}
for len(authorizedKeysBytes) > 0 {
authorizedPubKey, _, _, restBytes, err := parseAuthorizedKey(authorizedKeysBytes)
if err != nil {
if dlog.Server != nil {
dlog.Server.Warn(user, "Skipping unparseable authorized_keys line", err)
}
nextAuthorizedKeysBytes, ok := advanceToNextAuthorizedKeysLine(authorizedKeysBytes)
if !ok {
break
}
authorizedKeysBytes = nextAuthorizedKeysBytes
continue
}
authorizedKeysMap[string(authorizedPubKey.Marshal())] = true
authorizedKeysBytes = restBytes
if dlog.Server != nil {
dlog.Server.Debug(user, "Authorized public key fingerprint",
gossh.FingerprintSHA256(authorizedPubKey))
}
}
if dlog.Server != nil {
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 advanceToNextAuthorizedKeysLine(authorizedKeysBytes []byte) ([]byte, bool) {
lineEnd := bytes.IndexByte(authorizedKeysBytes, '\n')
if lineEnd == -1 {
return nil, false
}
nextBytes := authorizedKeysBytes[lineEnd+1:]
return nextBytes, true
}
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. An absolute
// CacheDir (as used by the BSD packages, e.g. /var/run/dserver/cache)
// must be used as-is: joining it with the CWD would break auth
// whenever dserver is started from a directory other than / (e.g. a
// manual rc.d restart from a home directory). Relative CacheDirs stay
// relative to the CWD as before.
if cacheDir != "" {
cacheBase := cacheDir
if !filepath.IsAbs(cacheDir) {
cacheBase = filepath.Join(cwd, cacheDir)
}
cachePath := filepath.Join(cacheBase, 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")
}
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