e827763f2e
This fixes a few issues I have found reviewing the code: 1) Limit the amount of data ReadLongName() will read. Previously, you could send gocryptfs into out-of-memory by symlinking gocryptfs.diriv to /dev/zero. 2) Handle the empty input case in unPad16() by returning an error. Previously, it would panic with an out-of-bounds array read. It is unclear to me if this could actually be triggered. 3) Reject empty names after base64-decoding in DecryptName(). An empty name crashes emeCipher.Decrypt(). It is unclear to me if B64.DecodeString() can actually return a non-error empty result, but let's guard against it anyway.
84 lines
2.5 KiB
Go
84 lines
2.5 KiB
Go
// Package nametransform encrypts and decrypts filenames.
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package nametransform
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import (
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"bytes"
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"crypto/aes"
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"encoding/base64"
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"syscall"
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"github.com/rfjakob/eme"
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"github.com/rfjakob/gocryptfs/internal/tlog"
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)
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// NameTransform is used to transform filenames.
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type NameTransform struct {
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emeCipher *eme.EMECipher
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longNames bool
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DirIVCache dirIVCache
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// B64 = either base64.URLEncoding or base64.RawURLEncoding, depeding
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// on the Raw64 feature flag
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B64 *base64.Encoding
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}
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// New returns a new NameTransform instance.
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func New(e *eme.EMECipher, longNames bool, raw64 bool) *NameTransform {
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b64 := base64.URLEncoding
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if raw64 {
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b64 = base64.RawURLEncoding
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}
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return &NameTransform{
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emeCipher: e,
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longNames: longNames,
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B64: b64,
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}
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}
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// DecryptName decrypts a base64-encoded encrypted filename "cipherName" using the
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// initialization vector "iv".
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func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
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bin, err := n.B64.DecodeString(cipherName)
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if err != nil {
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return "", err
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}
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if len(bin) == 0 {
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tlog.Warn.Printf("DecryptName: empty input")
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return "", syscall.EBADMSG
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}
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if len(bin)%aes.BlockSize != 0 {
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tlog.Debug.Printf("DecryptName %q: decoded length %d is not a multiple of 16", cipherName, len(bin))
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return "", syscall.EBADMSG
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}
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bin = n.emeCipher.Decrypt(iv, bin)
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bin, err = unPad16(bin)
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if err != nil {
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tlog.Debug.Printf("DecryptName: unPad16 error detail: %v", err)
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// unPad16 returns detailed errors including the position of the
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// incorrect bytes. Kill the padding oracle by lumping everything into
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// a generic error.
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return "", syscall.EBADMSG
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}
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// A name can never contain a null byte or "/". Make sure we never return those
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// to the kernel, even when we read a corrupted (or fuzzed) filesystem.
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if bytes.Contains(bin, []byte{0}) || bytes.Contains(bin, []byte("/")) {
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return "", syscall.EBADMSG
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}
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plain := string(bin)
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return plain, err
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}
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// EncryptName encrypts "plainName", returns a base64-encoded "cipherName64".
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// Used internally by EncryptPathDirIV().
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// The encryption is either CBC or EME, depending on "useEME".
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//
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// This function is exported because fusefrontend needs access to the full (not hashed)
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// name if longname is used. Otherwise you should use EncryptPathDirIV()
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func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 string) {
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bin := []byte(plainName)
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bin = pad16(bin)
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bin = n.emeCipher.Encrypt(iv, bin)
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cipherName64 = n.B64.EncodeToString(bin)
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return cipherName64
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}
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