Re: [PATCH net v4] net: nfc: nci: Fix parameter validation for packet data

[Michael Thalmeier <michael.thalmeier@hale.at>]

Am 08.01.26 um 03:15 schrieb Jakub Kicinski:
> On Wed, 7 Jan 2026 11:06:27 +0100 Michael Thalmeier wrote:
>>>> @@ -380,6 +384,10 @@ static int nci_rf_discover_ntf_packet(struct nci_dev *ndev,
>>>>    	pr_debug("rf_tech_specific_params_len %d\n",
>>>>    		 ntf.rf_tech_specific_params_len);
>>>>    
>>>> +	if (skb->len < (data - skb->data) +
>>>> +			ntf.rf_tech_specific_params_len + sizeof(ntf.ntf_type))
>>>> +		return -EINVAL;
>>>
>>> Are we validating ntf.rf_tech_specific_params_len against the
>>> extraction logic in nci_extract_rf_params_nfca_passive_poll()
>>> and friends?
>>
>> You are right. The current patch is only validating that the received
>> packet is consistent in the way that the rf_tech_specific_params_len
>> number of bytes is also contained in the buffer.
>>
>> There is currently no code that validates that
>> nci_extract_rf_params_nfca_passive_poll and friends only access the
>> given number of bytes in their logic.
>> And to be frank, I do not know how to implement this without either
>> cluttering the code with validation logic or re-implementing half the
>> parsing logic for length validation.
> 
> Don't think there's a magic bullet, we'd either have to pass the skb
> or "remaining length" to all the parsing helpers and have them ensure
> they are not going out of bounds.
> 
> There doesn't seem to be a huge number of those helpers but if you
> don't wanna tackle trying to validate the accesses maybe just add a
> couple of comments that the validation is missing in the helpers called
> in the switch statement?

Will be sending an updated patch with validation in the helpers.

> 
> BTW are you actually using the Linux NFC implementation or just playing
> with it? I'm not sure I'd trust this code for anything but accumulating
> C-V-Es, TBH.

Yes, we are using the Linux NFC implementation with the NCI driver (with 
a NXP PN7150 NFC chip) in production devices. It was actually working 
quite well and stable until the referenced commit completely broke it.