Re: [PATCH v2] nfc: pn533: Add poll mod list filling check

[Krzysztof Kozlowski <krzk@kernel.org>]

On 29/08/2024 10:26, Paolo Abeni wrote:
> 
> 
> On 8/27/24 10:48, Aleksandr Mishin wrote:
>> In case of im_protocols value is 1 and tm_protocols value is 0 this
>> combination successfully passes the check
>> 'if (!im_protocols && !tm_protocols)' in the nfc_start_poll().
>> But then after pn533_poll_create_mod_list() call in pn533_start_poll()
>> poll mod list will remain empty and dev->poll_mod_count will remain 0
>> which lead to division by zero.
>>
>> Normally no im protocol has value 1 in the mask, so this combination is
>> not expected by driver. But these protocol values actually come from
>> userspace via Netlink interface (NFC_CMD_START_POLL operation). So a
>> broken or malicious program may pass a message containing a "bad"
>> combination of protocol parameter values so that dev->poll_mod_count
>> is not incremented inside pn533_poll_create_mod_list(), thus leading
>> to division by zero.
>> Call trace looks like:
>> nfc_genl_start_poll()
>>    nfc_start_poll()
>>      ->start_poll()
>>      pn533_start_poll()
>>
>> Add poll mod list filling check.
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Fixes: dfccd0f58044 ("NFC: pn533: Add some polling entropy")
>> Signed-off-by: Aleksandr Mishin <amishin@t-argos.ru>
> 
> The issue looks real to me and the proposed fix the correct one, but 
> waiting a little more for Krzysztof feedback, as he expressed concerns 
> on v1.

There was one month delay between my reply and clarifications from
Fedor, so original patch is neither in my mailbox nor in my brain.


Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

However different problem is: shouldn't as well or instead
nfc_genl_start_poll() validate the attributes received by netlink?

We just pass them directly to the drivers and several other drivers
might not expect random stuff there.

Best regards,
Krzysztof