Re: [PATCH] dmaengine: usb-dmac: Avoid format-overflow warning

[Lad, Prabhakar]

Hi Kees,

Thank you for the review.

On Wed, Jan 10, 2024 at 10:41 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Wed, Jan 10, 2024 at 10:22:10PM +0000, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> >
> > gcc points out that the fix-byte buffer might be too small:
> > drivers/dma/sh/usb-dmac.c: In function 'usb_dmac_probe':
> > drivers/dma/sh/usb-dmac.c:720:34: warning: '%u' directive writing between 1 and 10 bytes into a region of size 3 [-Wformat-overflow=]
> >   720 |         sprintf(pdev_irqname, "ch%u", index);
> >       |                                  ^~
> > In function 'usb_dmac_chan_probe',
> >     inlined from 'usb_dmac_probe' at drivers/dma/sh/usb-dmac.c:814:9:
> > drivers/dma/sh/usb-dmac.c:720:31: note: directive argument in the range [0, 4294967294]
> >   720 |         sprintf(pdev_irqname, "ch%u", index);
> >       |                               ^~~~~~
> > drivers/dma/sh/usb-dmac.c:720:9: note: 'sprintf' output between 4 and 13 bytes into a destination of size 5
> >   720 |         sprintf(pdev_irqname, "ch%u", index);
> >       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Maximum number of channels for USB-DMAC as per the driver is 1-99 so use
> > u8 instead of unsigned int/int for DMAC channel indexing and make the
> > pdev_irqname string long enough to avoid the warning.
> >
> > While at it use scnprintf() instead of sprintf() to make the code more
> > robust.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
>
> This looks like good fixes; thanks! I see n_channels is sanity checked
> during the probe in usb_dmac_chan_probe(), so this looks good.
>
> (Is there a reason not to also change n_channels to a u8?)
>
Good point, I oversighted it by just looking at the loop indices. I
will send a v2 with that change.

Cheers,
Prabhakar

> -Kees
>
> > ---
> >  drivers/dma/sh/usb-dmac.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/dma/sh/usb-dmac.c b/drivers/dma/sh/usb-dmac.c
> > index a9b4302f6050..f7cd0cad056c 100644
> > --- a/drivers/dma/sh/usb-dmac.c
> > +++ b/drivers/dma/sh/usb-dmac.c
> > @@ -706,10 +706,10 @@ static const struct dev_pm_ops usb_dmac_pm = {
> >
> >  static int usb_dmac_chan_probe(struct usb_dmac *dmac,
> >                              struct usb_dmac_chan *uchan,
> > -                            unsigned int index)
> > +                            u8 index)
> >  {
> >       struct platform_device *pdev = to_platform_device(dmac->dev);
> > -     char pdev_irqname[5];
> > +     char pdev_irqname[6];
> >       char *irqname;
> >       int ret;
> >
> > @@ -717,7 +717,7 @@ static int usb_dmac_chan_probe(struct usb_dmac *dmac,
> >       uchan->iomem = dmac->iomem + USB_DMAC_CHAN_OFFSET(index);
> >
> >       /* Request the channel interrupt. */
> > -     sprintf(pdev_irqname, "ch%u", index);
> > +     scnprintf(pdev_irqname, sizeof(pdev_irqname), "ch%u", index);
> >       uchan->irq = platform_get_irq_byname(pdev, pdev_irqname);
> >       if (uchan->irq < 0)
> >               return -ENODEV;
> > @@ -768,8 +768,8 @@ static int usb_dmac_probe(struct platform_device *pdev)
> >       const enum dma_slave_buswidth widths = USB_DMAC_SLAVE_BUSWIDTH;
> >       struct dma_device *engine;
> >       struct usb_dmac *dmac;
> > -     unsigned int i;
> >       int ret;
> > +     u8 i;
> >
> >       dmac = devm_kzalloc(&pdev->dev, sizeof(*dmac), GFP_KERNEL);
> >       if (!dmac)
> > @@ -869,7 +869,7 @@ static void usb_dmac_chan_remove(struct usb_dmac *dmac,
> >  static void usb_dmac_remove(struct platform_device *pdev)
> >  {
> >       struct usb_dmac *dmac = platform_get_drvdata(pdev);
> > -     int i;
> > +     u8 i;
> >       for (i = 0; i < dmac->n_channels; ++i)
> >               usb_dmac_chan_remove(dmac, &dmac->channels[i]);
> > --
> > 2.34.1
> >
>
> --
> Kees Cook