linux-kernel - Re: [PATCH] nfc: pn533: Add poll mod list filling check

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Message-ID: <4899faf4-14cc-4e68-86e5-8745b38e5ab1@t-argos.ru>
Date: Wed, 3 Jul 2024 10:26:31 +0300
From: Aleksandr Mishin <amishin@...rgos.ru>
To: Krzysztof Kozlowski <krzk@...nel.org>, Samuel Ortiz
	<sameo@...ux.intel.com>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<lvc-project@...uxtesting.org>
Subject: Re: [PATCH] nfc: pn533: Add poll mod list filling check



On 03.07.2024 8:02, Krzysztof Kozlowski wrote:
> On 02/07/2024 11:39, Aleksandr Mishin wrote:
>> In case of im_protocols value is 1 and tm_protocols value is 0 this
> 
> Which im protocol has value 1 in the mask?
> 
> The pn533_poll_create_mod_list() handles all possible masks, so your
> case is just not possible to happen.

Exactly. pn533_poll_create_mod_list() handles all possible specified 
masks. No im protocol has value 1 in the mask. In case of 'im_protocol' 
parameter has value of 1, no mod will be added. So dev->poll_mod_count 
will remain 0.
I assume 'im_protocol' parameter is "external" to this driver, it comes 
from outside and can contain any value, so driver has to be able to 
protect itself from incorrect values.

> 
> This patch is purely to satisfy (your) static analyzers, so this should
> be clear in commit msg. You are not fixing any bug but adding sort of
> defensive code and suppresion of false-positive warning...
> 
>> 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.
>>
>> 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@...rgos.ru>
>> ---
>>   drivers/nfc/pn533/pn533.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/nfc/pn533/pn533.c b/drivers/nfc/pn533/pn533.c
>> index b19c39dcfbd9..e2bc67300a91 100644
>> --- a/drivers/nfc/pn533/pn533.c
>> +++ b/drivers/nfc/pn533/pn533.c
>> @@ -1723,6 +1723,11 @@ static int pn533_start_poll(struct nfc_dev *nfc_dev,
>>   	}
>>   
>>   	pn533_poll_create_mod_list(dev, im_protocols, tm_protocols);
>> +	if (!dev->poll_mod_count) {
>> +		nfc_err(dev->dev,
>> +			"Poll mod list is empty\n");
> 
> Odd wrapping.

Just like other messages in this function.

> 
>> +		return -EINVAL;
>> +	}
>>   
>>   	/* Do not always start polling from the same modulation */
>>   	get_random_bytes(&rand_mod, sizeof(rand_mod));
> 
> Best regards,
> Krzysztof
> 

-- 
Kind regards
Aleksandr