Re: [PATCH v3] iio: backend: fix out-of-bound write

["Nuno Sá" <noname.nuno@gmail.com>]

On Tue, 2025-05-06 at 12:00 -0500, David Lechner wrote:
> On 5/5/25 3:38 PM, Markus Burri wrote:
> > The buffer is set to 80 character. If a caller write more characters,
> > count is truncated to the max available space in "simple_write_to_buffer".
> > But afterwards a string terminator is written to the buffer at offset count
> > without boundary check. The zero termination is written OUT-OF-BOUND.
> > 
> > Add a check that the given buffer is smaller then the buffer to prevent.
> > 
> > Fixes: 035b4989211d ("iio: backend: make sure to NULL terminate stack buffer")
> > Signed-off-by: Markus Burri <markus.burri@mt.com>
> > ---
> >  drivers/iio/industrialio-backend.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-
> > backend.c
> > index a43c8d1bb3d0..4a364e038449 100644
> > --- a/drivers/iio/industrialio-backend.c
> > +++ b/drivers/iio/industrialio-backend.c
> > @@ -155,11 +155,14 @@ static ssize_t iio_backend_debugfs_write_reg(struct file
> > *file,
> >  	ssize_t rc;
> >  	int ret;
> >  
> > +	if (count >= sizeof(buf) - 1)
> 
> Isn't it OK if count == sizeof(buf) - 1? In other words, should be:
> 
> 	if (count >= sizeof(buf))

Oh, indeed you're right. Sorry Mark! I was the one asking for it but I did not
realized the comparison was '>='. So I was thinking if (count > sizeof(buf) - 1)
which is pretty much if (count >= sizeof(buf))

Arghh... Maybe Jonathan can tweak this while applying so you do not have to spin
another version because of this.

- Nuno Sá

> 
> > +		return -ENOSPC;
> > +
> >  	rc = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf, count);
> >  	if (rc < 0)
> >  		return rc;
> >  
> > -	buf[count] = '\0';
> > +	buf[rc] = '\0';
> >  
> >  	ret = sscanf(buf, "%i %i", &back->cached_reg_addr, &val);
> >  
> > 
> > base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e
> 
> It looks like we have the same or similar bugs in:
> 
> drivers/accel/ivpu/ivpu_debugfs.c
> drivers/gpio/gpio-virtuser.c
> drivers/iio/industrialio-core.c
> drivers/iio/dac/ad3552r-hs.c
> 
> Do you plan to fix these as well?