Re: [PATCH 1/2] iio: backend: make sure to NULL terminate stack buffer

["Nuno Sá" <noname.nuno@gmail.com>]

On Tue, 2025-02-18 at 09:52 -0600, David Lechner wrote:
> On 2/18/25 4:31 AM, Nuno Sá via B4 Relay wrote:
> > From: Nuno Sá <nuno.sa@analog.com>
> > 
> > Make sure to NULL terminate the buffer in
> > iio_backend_debugfs_write_reg() before passing it to sscanf(). It is a
> > stack variable so we should not assume it will 0 initialized.
> > 
> > Fixes: cdf01e0809a4 ("iio: backend: add debugFs interface")
> > Signed-off-by: Nuno Sá <nuno.sa@analog.com>
> > ---
> >  drivers/iio/industrialio-backend.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-
> > backend.c
> > index
> > d4ad36f54090204bf3bef08457d4aa55aa7c11fc..a43c8d1bb3d0f4dda4277cac94b0ea9232
> > c071e4 100644
> > --- a/drivers/iio/industrialio-backend.c
> > +++ b/drivers/iio/industrialio-backend.c
> > @@ -155,10 +155,12 @@ static ssize_t iio_backend_debugfs_write_reg(struct
> > file *file,
> >  	ssize_t rc;
> >  	int ret;
> >  
> > -	rc = simple_write_to_buffer(buf, sizeof(buf), ppos, userbuf,
> > count);
> > +	rc = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf,
> > count);
> >  	if (rc < 0)
> >  		return rc;
> >  
> > +	buf[count] = '\0';
> 
> Does this need to be count++? Later we return count.
> 

Don't think so... count comes down from userspace. The termination is local so
we do not want to return count + 1 when userspace only requested to write count.
Same deal as in iio_debugfs_write_reg()

Also note that we pass sizeof(buf) - 1 into simple_write_to_buffer()

- Nuno Sá
>