netdev - Re: [PATCH net-next v2] net: nfc: Propagate ISO14443 type A target ATS to userspace via netlink

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Message-ID: <866ca6e3-1ea4-47ad-8df3-a8ab9604d48d@redhat.com>
Date: Thu, 7 Nov 2024 10:31:03 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Juraj Šarinay <juraj@...inay.com>,
 Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, krzk@...nel.org, kuba@...nel.org
Subject: Re: [PATCH net-next v2] net: nfc: Propagate ISO14443 type A target
 ATS to userspace via netlink



On 11/6/24 15:58, Juraj Šarinay wrote:
> On Wed, 2024-11-06 at 10:18 +0000, Simon Horman wrote:
>>> Add a 20-byte field ats to struct nfc_target and expose it as
>>> NFC_ATTR_TARGET_ATS via the netlink interface. The payload contains
>>> 'historical bytes' that help to distinguish cards from one another.
>>> The information is commonly used to assemble an emulated ATR similar
>>> to that reported by smart cards with contacts.
>>
>> Perhaps I misunderstand things, and perhaps there is precedence in relation
>> to ATR_RES. But I am slightly concerned that this leans towards exposing
>> internal details rather then semantics via netlink.
>>
> 
> Hi Simon
> 
> Thanks for the feedback. NFC_ATTR_TARGET_ATS would serve a similar
> purpose as the following attributes the kernel already exposes (see
> nfc.h):
> 
>  * @NFC_ATTR_TARGET_SENS_RES: NFC-A targets extra information such as NFCID
>  * @NFC_ATTR_TARGET_SEL_RES: NFC-A targets extra information (useful if the
>  *	target is not NFC-Forum compliant)
>  * @NFC_ATTR_TARGET_NFCID1: NFC-A targets identifier, max 10 bytes
>  * @NFC_ATTR_TARGET_SENSB_RES: NFC-B targets extra information, max 12 bytes
>  * @NFC_ATTR_TARGET_SENSF_RES: NFC-F targets extra information, max 18 bytes
>  * @NFC_ATTR_TARGET_ISO15693_DSFID: ISO 15693 Data Storage Format Identifier
>  * @NFC_ATTR_TARGET_ISO15693_UID: ISO 15693 Unique Identifier
> 
> The ATR I am after means "Answer To Reset" as defined in ISO 7816. It
> has little to do with ATR_RES := "Attribute Request Response" defined
> in the NFC Digital specification. I only mentioned ATR_RES as the
> source of the information handled by nci_store_general_bytes_nfc_dep(),
> the function that motivated some of the code I propose to add.
> 
> Part 3 of the PC/SC Specification, Section 3.1.3.2.3 on ATR may perhaps
> serve as a more authoritative source of motivation for the patch.
> 
> https://pcscworkgroup.com/Download/Specifications/pcsc3_v2.01.09.pdf
> 
> The goal is to access contactless identification cards via PC/SC.

Makes sense, thanks for the additional details.

Small nit: you should have retained Krzysztof tag from from v1.

No need to repost.

Thanks,

Paolo