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

[Aleksandr Mishin]

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@xxxxxxxxxx>
> > ---
> >   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