fusefrontend: allow slashes in xattr names

xattr names have fewer restrictions than file names,
relax the validation.

Fixes https://github.com/rfjakob/gocryptfs/issues/627

5 files changed, 96 insertions, 16 deletions

diff --git a/internal/fusefrontend/node_xattr.go b/internal/fusefrontend/node_xattr.go
index 09ee5ef..44bc502 100644
--- a/internal/fusefrontend/node_xattr.go
+++ b/internal/fusefrontend/node_xattr.go
@@ -15,10 +15,6 @@ import (
 // -1 as uint32
 const minus1 = ^uint32(0)
 
-// xattr names are encrypted like file names, but with a fixed IV.
-// Padded with "_xx" for length 16.
-var xattrNameIV = []byte("xattr_name_iv_xx")
-
 // We store encrypted xattrs under this prefix plus the base64-encoded
 // encrypted original name.
 var xattrStorePrefix = "user.gocryptfs."
diff --git a/internal/fusefrontend/root_node.go b/internal/fusefrontend/root_node.go
index 7221be6..39cdef7 100644
--- a/internal/fusefrontend/root_node.go
+++ b/internal/fusefrontend/root_node.go
@@ -268,7 +268,7 @@ func (rn *RootNode) decryptXattrValue(cData []byte) (data []byte, err error) {
 // encryptXattrName transforms "user.foo" to "user.gocryptfs.a5sAd4XAa47f5as6dAf"
 func (rn *RootNode) encryptXattrName(attr string) (string, error) {
 	// xattr names are encrypted like file names, but with a fixed IV.
-	cAttr, err := rn.nameTransform.EncryptName(attr, xattrNameIV)
+	cAttr, err := rn.nameTransform.EncryptXattrName(attr)
 	if err != nil {
 		return "", err
 	}
@@ -282,7 +282,7 @@ func (rn *RootNode) decryptXattrName(cAttr string) (attr string, err error) {
 	}
 	// Strip "user.gocryptfs." prefix
 	cAttr = cAttr[len(xattrStorePrefix):]
-	attr, err = rn.nameTransform.DecryptName(cAttr, xattrNameIV)
+	attr, err = rn.nameTransform.DecryptXattrName(cAttr)
 	if err != nil {
 		return "", err
 	}
diff --git a/internal/nametransform/names.go b/internal/nametransform/names.go
index e07ccfb..ebe0fb6 100644
--- a/internal/nametransform/names.go
+++ b/internal/nametransform/names.go
@@ -66,7 +66,14 @@ func New(e *eme.EMECipher, longNames bool, longNameMax uint8, raw64 bool, badnam
 func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
 	res, err := n.decryptName(cipherName, iv)
 	if err != nil && n.HaveBadnamePatterns() {
-		return n.decryptBadname(cipherName, iv)
+		res, err = n.decryptBadname(cipherName, iv)
+	}
+	if err != nil {
+		return "", err
+	}
+	if err := IsValidName(res); err != nil {
+		tlog.Warn.Printf("DecryptName %q: invalid name after decryption: %v", cipherName, err)
+		return "", syscall.EBADMSG
 	}
 	return res, err
 }
@@ -79,30 +86,29 @@ func (n *NameTransform) decryptName(cipherName string, iv []byte) (string, error
 		return "", err
 	}
 	if len(bin) == 0 {
-		tlog.Warn.Printf("DecryptName: empty input")
+		tlog.Warn.Printf("decryptName: empty input")
 		return "", syscall.EBADMSG
 	}
 	if len(bin)%aes.BlockSize != 0 {
-		tlog.Debug.Printf("DecryptName %q: decoded length %d is not a multiple of 16", cipherName, len(bin))
+		tlog.Debug.Printf("decryptName %q: decoded length %d is not a multiple of 16", cipherName, len(bin))
 		return "", syscall.EBADMSG
 	}
 	bin = n.emeCipher.Decrypt(iv, bin)
 	bin, err = unPad16(bin)
 	if err != nil {
-		tlog.Warn.Printf("DecryptName %q: unPad16 error: %v", cipherName, err)
+		tlog.Warn.Printf("decryptName %q: unPad16 error: %v", cipherName, err)
 		return "", syscall.EBADMSG
 	}
 	plain := string(bin)
-	if err := IsValidName(plain); err != nil {
-		tlog.Warn.Printf("DecryptName %q: invalid name after decryption: %v", cipherName, err)
-		return "", syscall.EBADMSG
-	}
 	return plain, err
 }
 
-// EncryptName encrypts "plainName", returns a base64-encoded "cipherName64",
+// EncryptName encrypts a file name "plainName" and returns a base64-encoded "cipherName64",
 // encrypted using EME (https://github.com/rfjakob/eme).
 //
+// plainName is checked for null bytes, slashes etc. and such names are rejected
+// with an 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, err error) {
@@ -110,11 +116,19 @@ func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 s
 		tlog.Warn.Printf("EncryptName %q: invalid plainName: %v", plainName, err)
 		return "", syscall.EBADMSG
 	}
+	return n.encryptName(plainName, iv), nil
+}
+
+// encryptName encrypts "plainName" and returns a base64-encoded "cipherName64",
+// encrypted using EME (https://github.com/rfjakob/eme).
+//
+// No checks for null bytes etc are performed against plainName.
+func (n *NameTransform) encryptName(plainName string, iv []byte) (cipherName64 string) {
 	bin := []byte(plainName)
 	bin = pad16(bin)
 	bin = n.emeCipher.Encrypt(iv, bin)
 	cipherName64 = n.B64.EncodeToString(bin)
-	return cipherName64, nil
+	return cipherName64
 }
 
 // EncryptAndHashName encrypts "name" and hashes it to a longname if it is
diff --git a/internal/nametransform/names_test.go b/internal/nametransform/names_test.go
index b4e98d4..3c26c43 100644
--- a/internal/nametransform/names_test.go
+++ b/internal/nametransform/names_test.go
@@ -75,3 +75,26 @@ func TestIsValidName(t *testing.T) {
 		}
 	}
 }
+
+func TestIsValidXattrName(t *testing.T) {
+	cases := []struct {
+		in   string
+		want bool
+	}{
+		{"", false},
+		{".", true},
+		{"..", true},
+		{"...", true},
+		{"asdasd/asdasd", true},
+		{"asdasd\000asdasd", false},
+		{"hello", true},
+		{strings.Repeat("x", 255), true},
+		{strings.Repeat("x", 256), true},
+	}
+	for _, c := range cases {
+		have := isValidXattrName(c.in)
+		if (have == nil) != c.want {
+			t.Errorf("isValidXattrName(%q): want %v have %v", c.in, c.want, have)
+		}
+	}
+}
diff --git a/internal/nametransform/xattr.go b/internal/nametransform/xattr.go
new file mode 100644
index 0000000..0aa0fd8
--- /dev/null
+++ b/internal/nametransform/xattr.go
@@ -0,0 +1,47 @@
+package nametransform
+
+import (
+	"fmt"
+	"strings"
+	"syscall"
+
+	"github.com/rfjakob/gocryptfs/v2/internal/tlog"
+)
+
+// xattr names are encrypted like file names, but with a fixed IV.
+// Padded with "_xx" for length 16.
+var xattrNameIV = []byte("xattr_name_iv_xx")
+
+func isValidXattrName(name string) error {
+	if name == "" {
+		return fmt.Errorf("empty input")
+	}
+	if strings.Contains(name, "\000") {
+		return fmt.Errorf("contains forbidden null byte")
+	}
+	return nil
+}
+
+// EncryptXattrName encrypts an extended attribute (xattr) name.
+// xattr names are encrypted like file names, but with a fixed IV, and fewer
+// naming restriction.
+func (n *NameTransform) EncryptXattrName(plainName string) (cipherName64 string, err error) {
+	if err := isValidXattrName(plainName); err != nil {
+		tlog.Warn.Printf("EncryptXattrName %q: invalid plainName: %v", plainName, err)
+		return "", syscall.EBADMSG
+	}
+	return n.encryptName(plainName, xattrNameIV), nil
+}
+
+// DecryptName calls decryptName to try and decrypt a base64-encoded encrypted
+// filename "cipherName", and failing that checks if it can be bypassed
+func (n *NameTransform) DecryptXattrName(cipherName string) (plainName string, err error) {
+	if plainName, err = n.decryptName(cipherName, xattrNameIV); err != nil {
+		return "", err
+	}
+	if err := isValidXattrName(plainName); err != nil {
+		tlog.Warn.Printf("DecryptXattrName %q: invalid name after decryption: %v", cipherName, err)
+		return "", syscall.EBADMSG
+	}
+	return plainName, err
+}