linux-kernel - Re: [PATCH 10/18] tty: serial: samsung: make max

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Message-ID: <CAPLW+4=G0+Vuwm0Jdp4wxbL9aUTaM8S+srXYwYkm10K+=hXbOg@mail.gmail.com>
Date: Wed, 17 Jan 2024 10:26:03 -0600
From: Sam Protsenko <semen.protsenko@...aro.org>
To: André Draszik <andre.draszik@...aro.org>
Cc: Tudor Ambarus <tudor.ambarus@...aro.org>, krzysztof.kozlowski@...aro.org, 
	alim.akhtar@...sung.com, gregkh@...uxfoundation.org, jirislaby@...nel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org, 
	peter.griffin@...aro.org, kernel-team@...roid.com, willmcvicker@...gle.com
Subject: Re: [PATCH 10/18] tty: serial: samsung: make max_count unsigned int

On Wed, Jan 17, 2024 at 9:38 AM André Draszik <andre.draszik@...aro.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 AM Tudor Ambarus <tudor.ambarus@...aro.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@...aro.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 = &ourport->port;
> > > > +       unsigned int max_count = 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 first, 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 completing the
> while() (always, no matter what start-value max_count had)
>
> Cheers,
> Andre'
>