eCryptfs: Remove buggy and unnecessary write in file name decode routine

Dmitry Chernenkov used KASAN to discover that eCryptfs writes past the
end of the allocated buffer during encrypted filename decoding. This
fix corrects the issue by getting rid of the unnecessary 0 write when
the current bit offset is 2.
Signed-off-by: NMichael Halcrow <mhalcrow@google.com>
Reported-by: NDmitry Chernenkov <dmitryc@google.com>
Suggested-by: NKees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org # v2.6.29+: 51ca58dc eCryptfs: Filename Encryption: Encoding and encryption functions
Signed-off-by: NTyler Hicks <tyhicks@canonical.com>

fs/ecryptfs/crypto.c

@@ -1917,7 +1917,6 @@ ecryptfs_decode_from_filename(unsigned char *dst, size_t *dst_size,
 			break;
 		case 2:
 			dst[dst_byte_offset++] |= (src_byte);
-			dst[dst_byte_offset] = 0;
 			current_bit_offset = 0;
 			break;
 		}