nametransform: check name validity on encryption

xfstests generic/523 discovered that we allowed to set
xattrs with "/" in the name, but did not allow to read
them later.

With this change we do not allow to set them in the first
place.

5 files changed, 70 insertions, 18 deletions

diff --git a/internal/nametransform/diriv.go b/internal/nametransform/diriv.go
index b2f165b..1d27aa5 100644
--- a/internal/nametransform/diriv.go
+++ b/internal/nametransform/diriv.go
@@ -102,7 +102,10 @@ func (be *NameTransform) EncryptAndHashName(name string, iv []byte) (string, err
 	if len(name) > NameMax {
 		return "", syscall.ENAMETOOLONG
 	}
-	cName := be.EncryptName(name, iv)
+	cName, err := be.EncryptName(name, iv)
+	if err != nil {
+		return "", err
+	}
 	if be.longNames && len(cName) > NameMax {
 		return be.HashLongName(cName), nil
 	}
diff --git a/internal/nametransform/longnames.go b/internal/nametransform/longnames.go
index aa463a1..74ddb07 100644
--- a/internal/nametransform/longnames.go
+++ b/internal/nametransform/longnames.go
@@ -132,7 +132,10 @@ func (n *NameTransform) WriteLongNameAt(dirfd int, hashName string, plainName st
 	if err != nil {
 		return err
 	}
-	cName := n.EncryptName(plainName, dirIV)
+	cName, err := n.EncryptName(plainName, dirIV)
+	if err != nil {
+		return err
+	}
 
 	// Write the encrypted name into hashName.name
 	fdRaw, err := syscallcompat.Openat(dirfd, hashName+LongNameSuffix,
diff --git a/internal/nametransform/names.go b/internal/nametransform/names.go
index 119d592..ca28230 100644
--- a/internal/nametransform/names.go
+++ b/internal/nametransform/names.go
@@ -2,7 +2,6 @@
 package nametransform
 
 import (
-	"bytes"
 	"crypto/aes"
 	"encoding/base64"
 	"path/filepath"
@@ -21,7 +20,7 @@ const (
 // NameTransformer is an interface used to transform filenames.
 type NameTransformer interface {
 	DecryptName(cipherName string, iv []byte) (string, error)
-	EncryptName(plainName string, iv []byte) string
+	EncryptName(plainName string, iv []byte) (string, error)
 	EncryptAndHashName(name string, iv []byte) (string, error)
 	// HashLongName - take the hash of a long string "name" and return
 	// "gocryptfs.longname.[sha256]"
@@ -99,22 +98,14 @@ func (n *NameTransform) decryptName(cipherName string, iv []byte) (string, error
 	bin = n.emeCipher.Decrypt(iv, bin)
 	bin, err = unPad16(bin)
 	if err != nil {
-		tlog.Debug.Printf("DecryptName: unPad16 error detail: %v", err)
-		// unPad16 returns detailed errors including the position of the
-		// incorrect bytes. Kill the padding oracle by lumping everything into
-		// a generic error.
+		tlog.Warn.Printf("DecryptName %q: unPad16 error: %v", cipherName, err)
 		return "", syscall.EBADMSG
 	}
-	// A name can never contain a null byte or "/". Make sure we never return those
-	// to the kernel, even when we read a corrupted (or fuzzed) filesystem.
-	if bytes.Contains(bin, []byte{0}) || bytes.Contains(bin, []byte("/")) {
-		return "", syscall.EBADMSG
-	}
-	// The name should never be "." or "..".
-	if bytes.Equal(bin, []byte(".")) || bytes.Equal(bin, []byte("..")) {
+	plain := string(bin)
+	if err := IsValidName(plain); err != nil {
+		tlog.Warn.Printf("DecryptName %q: invalid name after decryption: %v", cipherName, err)
 		return "", syscall.EBADMSG
 	}
-	plain := string(bin)
 	return plain, err
 }
 
@@ -123,12 +114,16 @@ func (n *NameTransform) decryptName(cipherName string, iv []byte) (string, error
 //
 // This function is exported because in some cases, fusefrontend needs access
 // to the full (not hashed) name if longname is used.
-func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 string) {
+func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 string, err error) {
+	if err := IsValidName(plainName); err != nil {
+		tlog.Warn.Printf("EncryptName %q: invalid plainName: %v", plainName, err)
+		return "", syscall.EBADMSG
+	}
 	bin := []byte(plainName)
 	bin = pad16(bin)
 	bin = n.emeCipher.Encrypt(iv, bin)
 	cipherName64 = n.B64.EncodeToString(bin)
-	return cipherName64
+	return cipherName64, nil
 }
 
 // B64EncodeToString returns a Base64-encoded string
diff --git a/internal/nametransform/names_test.go b/internal/nametransform/names_test.go
index 9d77c2d..b4e98d4 100644
--- a/internal/nametransform/names_test.go
+++ b/internal/nametransform/names_test.go
@@ -2,6 +2,7 @@ package nametransform
 
 import (
 	"bytes"
+	"strings"
 	"testing"
 )
 
@@ -51,3 +52,26 @@ func TestUnpad16Garbage(t *testing.T) {
 		}
 	}
 }
+
+func TestIsValidName(t *testing.T) {
+	cases := []struct {
+		in   string
+		want bool
+	}{
+		{"", false},
+		{".", false},
+		{"..", false},
+		{"...", true},
+		{"asdasd/asdasd", false},
+		{"asdasd\000asdasd", false},
+		{"hello", true},
+		{strings.Repeat("x", 255), true},
+		{strings.Repeat("x", 256), false},
+	}
+	for _, c := range cases {
+		have := IsValidName(c.in)
+		if (have == nil) != c.want {
+			t.Errorf("IsValidName(%q): want %v have %v", c.in, c.want, have)
+		}
+	}
+}
diff --git a/internal/nametransform/valid.go b/internal/nametransform/valid.go
new file mode 100644
index 0000000..b991074
--- /dev/null
+++ b/internal/nametransform/valid.go
@@ -0,0 +1,27 @@
+package nametransform
+
+import (
+	"fmt"
+	"strings"
+)
+
+// IsValidName checks if `name` is a valid name for a normal file
+// (does not contain null bytes or "/" etc...).
+func IsValidName(name string) error {
+	if name == "" {
+		return fmt.Errorf("empty input")
+	}
+	if len(name) > NameMax {
+		return fmt.Errorf("too long")
+	}
+	// A name can never contain a null byte or "/". Make sure we never return those
+	// to the kernel, even when we read a corrupted (or fuzzed) filesystem.
+	if strings.Contains(name, "\000") || strings.Contains(name, "/") {
+		return fmt.Errorf("contains forbidden bytes")
+	}
+	// The name should never be "." or "..".
+	if name == "." || name == ".." {
+		return fmt.Errorf(". and .. are forbidden names")
+	}
+	return nil
+}