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crypt: check for maximum length before decrypting filename

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The EME Transform() method will panic if the input data is larger than
2048 bytes.

Fixes #2826
This commit is contained in:
Garry McNulty 2018-12-18 20:35:41 +00:00 committed by Nick Craig-Wood
parent c1dd76788d
commit 9cb3a68c38
2 changed files with 9 additions and 0 deletions
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4
backend/crypt/cipher.go
View File

@ -41,6 +41,7 @@ var (
ErrorBadDecryptControlChar = errors.New("bad decryption - contains control chars") ErrorBadDecryptControlChar = errors.New("bad decryption - contains control chars")
ErrorNotAMultipleOfBlocksize = errors.New("not a multiple of blocksize") ErrorNotAMultipleOfBlocksize = errors.New("not a multiple of blocksize")
ErrorTooShortAfterDecode = errors.New("too short after base32 decode") ErrorTooShortAfterDecode = errors.New("too short after base32 decode")
ErrorTooLongAfterDecode = errors.New("too long after base32 decode")
ErrorEncryptedFileTooShort = errors.New("file is too short to be encrypted") ErrorEncryptedFileTooShort = errors.New("file is too short to be encrypted")
ErrorEncryptedFileBadHeader = errors.New("file has truncated block header") ErrorEncryptedFileBadHeader = errors.New("file has truncated block header")
ErrorEncryptedBadMagic = errors.New("not an encrypted file - bad magic string") ErrorEncryptedBadMagic = errors.New("not an encrypted file - bad magic string")
@ -284,6 +285,9 @@ func (c *cipher) decryptSegment(ciphertext string) (string, error) {
// not possible if decodeFilename() working correctly // not possible if decodeFilename() working correctly
return "", ErrorTooShortAfterDecode return "", ErrorTooShortAfterDecode
} }
if len(rawCiphertext) > 2048 {
return "", ErrorTooLongAfterDecode
}
paddedPlaintext := eme.Transform(c.block, c.nameTweak[:], rawCiphertext, eme.DirectionDecrypt) paddedPlaintext := eme.Transform(c.block, c.nameTweak[:], rawCiphertext, eme.DirectionDecrypt)
plaintext, err := pkcs7.Unpad(nameCipherBlockSize, paddedPlaintext) plaintext, err := pkcs7.Unpad(nameCipherBlockSize, paddedPlaintext)
if err != nil { if err != nil {

5
backend/crypt/cipher_test.go
View File

@ -194,6 +194,10 @@ func TestEncryptSegment(t *testing.T) {
func TestDecryptSegment(t *testing.T) { func TestDecryptSegment(t *testing.T) {
// We've tested the forwards above, now concentrate on the errors // We've tested the forwards above, now concentrate on the errors
longName := make([]byte, 3328)
for i := range longName {
longName[i] = 'a'
}
c, _ := newCipher(NameEncryptionStandard, "", "", true) c, _ := newCipher(NameEncryptionStandard, "", "", true)
for _, test := range []struct { for _, test := range []struct {
in string in string
@ -201,6 +205,7 @@ func TestDecryptSegment(t *testing.T) {
}{ }{
{"64=", ErrorBadBase32Encoding}, {"64=", ErrorBadBase32Encoding},
{"!", base32.CorruptInputError(0)}, {"!", base32.CorruptInputError(0)},
{string(longName), ErrorTooLongAfterDecode},
{encodeFileName([]byte("a")), ErrorNotAMultipleOfBlocksize}, {encodeFileName([]byte("a")), ErrorNotAMultipleOfBlocksize},
{encodeFileName([]byte("123456789abcdef")), ErrorNotAMultipleOfBlocksize}, {encodeFileName([]byte("123456789abcdef")), ErrorNotAMultipleOfBlocksize},
{encodeFileName([]byte("123456789abcdef0")), pkcs7.ErrorPaddingTooLong}, {encodeFileName([]byte("123456789abcdef0")), pkcs7.ErrorPaddingTooLong},