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: Michael Halcrow <[email protected]>
Reported-by: Dmitry Chernenkov <[email protected]>
Suggested-by: Kees Cook <[email protected]>
Cc: [email protected] # v2.6.29+: 51ca58d eCryptfs: Filename Encryption: Encoding and encryption functions
Signed-off-by: Tyler Hicks <[email protected]>

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;
 		}