Problem

The function iso7816_process_fci() decodes the file_size tag (0x80) with sc_asn1_decode_integer(), so a msb set results into a negative value. I haven't found any hints in the ISO concerning the DO data field encoding for this tag. Cards I use encode them as 2 bytes hi-lo unsigned, not like ASN.1 integer.

Proposed Resolution

Use something like bebytes2ushort().

Steps to reproduce

In my case: 80 02 9E 98.

P:68283; T:0x139801973610560 14:05:22.810 [pkcs15-tool] reader-pcsc.c:335:pcsc_transmit: 
Incoming APDU (64 bytes):
62 3C 80 02 9E 98 82 05 04 41 61 A8 20 83 02 C0 b<.......Aa. ...
00 88 00 8A 01 05 AB 26 84 01 B2 84 01 B3 84 01 .......&........
A0 84 01 A1 90 00 84 01 DC 84 01 DD A0 10 A4 06 ................
95 01 08 83 01 00 A4 06 95 01 80 83 01 01 90 00 ................