Re: [PATCH v2] mlx4: fix a compilation warning in sysfs.c

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On Thu, Nov 22, 2018 at 12:26:59PM -0700, Jason Gunthorpe wrote:
> On Thu, Nov 15, 2018 at 08:10:36PM -0500, Qian Cai wrote:
> > drivers/infiniband/hw/mlx4/sysfs.c:360:2: warning: 'strncpy' output may be
> > truncated copying 8 bytes from a string of length 31 [-Wstringop-truncation]
> >
> > Signed-off-by: Qian Cai <cai@xxxxxx>
> >
> > Changes since v2:
> >  * Used strscpy() instead of snprintf()
> >  * Removed an unnecessary statement.
> >
> >  drivers/infiniband/hw/mlx4/sysfs.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/infiniband/hw/mlx4/sysfs.c b/drivers/infiniband/hw/mlx4/sysfs.c
> > index 752bdd536130..8cf0d2e4c823 100644
> > +++ b/drivers/infiniband/hw/mlx4/sysfs.c
> > @@ -357,8 +357,7 @@ static void get_name(struct mlx4_ib_dev *dev, char *name, int i, int max)
> >
> >  	/* pci_name format is: bus:dev:func -> xxxx:yy:zz.n */
> >  	strlcpy(name, pci_name(dev->dev->persist->pdev), max);
> > -	strncpy(base_name, name, 8); /*till xxxx:yy:*/
> > -	base_name[8] = '\0';
> > +	strscpy(base_name, name, sizeof(base_name)); /*till xxxx:yy:*/
> >  	/* with no ARI only 3 last bits are used so when the fn is higher than 8
> >  	 * need to add it to the dev num, so count in the last number will be
> >  	 * modulo 8 */
> >     	sprintf(name, "%s%.2d.%d", base_name, (i/8), (i%8));
>
> This whole routine is goofy. Why not just do something this:
>
> 	sprintf(name, "%.8s%.2d.%d", pci_name(dev->dev->persist->pdev), (i/8), (i%8));
>
> ?
>
> And while you are looking at this, the use of sprintf, not snprintf is
> wrong too, it should be snprintf(name, max, ...)

What is wrong with sprintf here?
base_name is limited, not controllable by user and NULL-terminated.

Thanks

>
> Jason

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