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Message-ID: <026bdf502c0af8260c67a7a851562633a6976031.camel@linaro.org>
Subject: Re: [PATCH 10/18] tty: serial: samsung: make max_count unsigned int
From: =?ISO-8859-1?Q?Andr=E9?= Draszik <andre.draszik@linaro.org>
To: Tudor Ambarus <tudor.ambarus@linaro.org>, Sam Protsenko
	 <semen.protsenko@linaro.org>
Cc: 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
Date: Wed, 17 Jan 2024 15:38:55 +0000
In-Reply-To: <b21a54a7-fe13-4a29-8e7e-6b653d5c24ef@linaro.org>
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>
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Hi,

On Wed, 2024-01-17 at 15:21 +0000, Tudor Ambarus wrote:
>=20
>=20
> On 1/16/24 18:21, Sam Protsenko wrote:
> > On Wed, Jan 10, 2024 at 4:23=E2=80=AFAM Tudor Ambarus <tudor.ambarus@li=
naro.org> wrote:
> > >=20
> > > ``max_count`` negative values are not used. Since ``port->fifosize``
> > > is an unsigned int, make ``max_count`` the same.
> > >=20
> > > Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> > > ---
> > > =C2=A0drivers/tty/serial/samsung_tty.c | 2 +-
> > > =C2=A01 file changed, 1 insertion(+), 1 deletion(-)
> > >=20
> > > diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/sa=
msung_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(vo=
id *dev_id)
> > > =C2=A0static void s3c24xx_serial_rx_drain_fifo(struct s3c24xx_uart_po=
rt *ourport)
> > > =C2=A0{
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct uart_port *port =3D=
 &ourport->port;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unsigned int max_count =3D port=
->fifosize;
> >=20
> > What if port->fifosize is 0? Then this code below:
> >=20
> > =C2=A0=C2=A0=C2=A0 while (max_count-- > 0) {
> >=20
> > would cause int overflow, if max_count is unsigned?
> >=20
>=20
> good catch, Sam!

Does it matter, though? As this is a post-decrement, the test is done first=
, and the
decrement after. Therefore, it'll still bail out as expected.

> I'm thinking of amending this and add at the beginning of the method:
>=20
> if (!max_count)
> 	return tty_flip_buffer_push(&port->state->port);

This will not help with overflow. It'll still have wrapped around after com=
pleting the
while() (always, no matter what start-value max_count had)

Cheers,
Andre'