Received-SPF: pass (google.com: domain of linux-kernel+bounces-29212-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240110102102.61587-1-tudor.ambarus@linaro.org>
 <20240110102102.61587-11-tudor.ambarus@linaro.org> <CAPLW+4=YYdUSaaLcsdEyPswC4s6onxuSh24vSfw4xys=sPZG_Q@mail.gmail.com>
 <b21a54a7-fe13-4a29-8e7e-6b653d5c24ef@linaro.org> <026bdf502c0af8260c67a7a851562633a6976031.camel@linaro.org>
In-Reply-To: <026bdf502c0af8260c67a7a851562633a6976031.camel@linaro.org>
From: Sam Protsenko <semen.protsenko@linaro.org>
Date: Wed, 17 Jan 2024 10:26:03 -0600
Message-ID: <CAPLW+4=G0+Vuwm0Jdp4wxbL9aUTaM8S+srXYwYkm10K+=hXbOg@mail.gmail.com>
Subject: Re: [PATCH 10/18] tty: serial: samsung: make max_count unsigned int
To: =?UTF-8?Q?Andr=C3=A9_Draszik?= <andre.draszik@linaro.org>
Cc: Tudor Ambarus <tudor.ambarus@linaro.org>, krzysztof.kozlowski@linaro.org, 
	alim.akhtar@samsung.com, gregkh@linuxfoundation.org, jirislaby@kernel.org, 
	linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, 
	peter.griffin@linaro.org, kernel-team@android.com, willmcvicker@google.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, Jan 17, 2024 at 9:38=E2=80=AFAM Andr=C3=A9 Draszik <andre.draszik@l=
inaro.org> wrote:
>
> Hi,
>
> On Wed, 2024-01-17 at 15:21 +0000, Tudor Ambarus wrote:
> >
> >
> > On 1/16/24 18:21, Sam Protsenko wrote:
> > > On Wed, Jan 10, 2024 at 4:23=E2=80=AFAM Tudor Ambarus <tudor.ambarus@=
linaro.org> wrote:
> > > >
> > > > ``max_count`` negative values are not used. Since ``port->fifosize`=
`
> > > > is an unsigned int, make ``max_count`` the same.
> > > >
> > > > Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> > > > ---
> > > >  drivers/tty/serial/samsung_tty.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/=
samsung_tty.c
> > > > index 90c49197efc7..dbbe6b8e3ceb 100644
> > > > --- a/drivers/tty/serial/samsung_tty.c
> > > > +++ b/drivers/tty/serial/samsung_tty.c
> > > > @@ -760,8 +760,8 @@ static irqreturn_t s3c24xx_serial_rx_chars_dma(=
void *dev_id)
> > > >  static void s3c24xx_serial_rx_drain_fifo(struct s3c24xx_uart_port =
*ourport)
> > > >  {
> > > >         struct uart_port *port =3D &ourport->port;
> > > > +       unsigned int max_count =3D port->fifosize;
> > >
> > > What if port->fifosize is 0? Then this code below:
> > >
> > >     while (max_count-- > 0) {
> > >
> > > would cause int overflow, if max_count is unsigned?
> > >
> >
> > good catch, Sam!
>
> Does it matter, though? As this is a post-decrement, the test is done fir=
st, and the
> decrement after. Therefore, it'll still bail out as expected.
>

Good catch on my good catch :)

> > I'm thinking of amending this and add at the beginning of the method:
> >
> > if (!max_count)
> >       return tty_flip_buffer_push(&port->state->port);
>
> This will not help with overflow. It'll still have wrapped around after c=
ompleting the
> while() (always, no matter what start-value max_count had)
>
> Cheers,
> Andre'
>