Re: [PATCH] iio: backend: fix uninitialized data in debugfs

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 9 Jun 2026 09:10:14 +0100
Nuno Sá <noname.nuno@gmail.com> wrote:

> On Mon, Jun 08, 2026 at 04:51:38PM -0500, Maxwell Doose wrote:
> > On Mon, 08 Jun 2026 21:31:14 +0100
> > Nuno Sá <noname.nuno@gmail.com> wrote:
> >   
> > > On Fri, 2026-06-05 at 11:28 +0300, Andy Shevchenko wrote:  
> > > > On Fri, Jun 05, 2026 at 09:12:38AM +0300, Dan Carpenter wrote:    
> > > > > On Thu, Jun 04, 2026 at 05:55:08PM +0300, Andy Shevchenko wrote:    
> > > > > > On Thu, Jun 04, 2026 at 01:42:11PM +0300, Dan Carpenter wrote:    
> > > > > > > On Thu, Jun 04, 2026 at 01:38:50PM +0300, Dan Carpenter wrote:    
> > > > > > > >    168          ret = sscanf(buf, "%i %i", &back->cached_reg_addr, &val);
> > > > > > > >                              ^^^
> > > > > > > > Uninitialized variable.    
> > > > > > > 
> > > > > > > s/variable/data/.    
> > > > > > 
> > > > > > With what I asked in the previous reply and what you explained there
> > > > > > (thanks, btw!) I still think your patches are not fully correct. They
> > > > > > will require to atomically write all or nothing. If we want support
> > > > > > partial writes we need to go with that differently (reset ppos when
> > > > > > we got enough or more than enough data).    
> > > > > 
> > > > > Requiring writes to syfs and debugfs be atomic is pretty normal and
> > > > > works well in practice.  These are very small writes.    
> > > > 
> > > > Perhaps. In any case your patch will break existing partial writes, right?
> > > > I'm still considering that resetting ppos is the right thing to do. Just
> > > > need to find where the best place is to do that.    
> > > 
> > > I think anyone doing partial writes on a debugfs interface like this one is very
> > > unlikely but it is a fair point, yes. But can't we be more relaxed on debugfs? No
> > > userspace app should be relying on debugfs in order to work (though I know that
> > > actually happens).
> > > 
> > > Anyways, this is one of those interesting edge cases and easy enough to get wrong. I
> > > guess we should either:
> > > 
> > > 1. Improve simple_write_to_buffer() docs;
> > > 2. Or come up with a new simple_write_once_to_buffer() helper?
> > >  
> > 
> > When you say "simple_write_once_to_buffer()" do you mean a wrapper
> > around simple_write_to_buffer() that also checks if *ppos is 0 and
> > returns -EINVAL if *ppos isn't 0? If so I can start writing that
> > function. Though I guess we probably want to ask Jonathan about it
> > first since obviously he'll have his own opinions.  
> 
> Yeah basically not allowing partial writes. Partial writes are also very
> tricky to handle in terms of concurrency (assuming userspace can do
> whatever they want). But I would not rush into writing the helper
> without understanding how people feel about it (at least the ones in
> this thread). Might not be super beneficial.

I'd be fine with such a helper.  No huge rush though as I don't plan
to back out the patch that kicked off this long discussion.
Hence it would be an improvement on top of that.   Dan probably is
the right person to offer a considered view on whether it is worth yet
another helper.

Jonathan

> 
> - Nuno Sá
> 
> > 
> > -- 
> > best regards,
> > max