Re: [PATCH 1/1] staging: ion: Prevent incorrect reference counting behavour

[Lee Jones <lee.jones@linaro.org>]

On Thu, 25 Nov 2021, Greg KH wrote:

> On Thu, Nov 25, 2021 at 01:03:46PM +0000, Lee Jones wrote:
> > On Thu, 25 Nov 2021, Greg KH wrote:
> > 
> > > On Thu, Nov 25, 2021 at 12:46:23PM +0000, Lee Jones wrote:
> > > > On Thu, 25 Nov 2021, Greg KH wrote:
> > > > 
> > > > > On Thu, Nov 25, 2021 at 12:02:34PM +0000, Lee Jones wrote:
> > > > > > Supply additional checks in order to prevent unexpected results.
> > > > > > 
> > > > > > Fixes: b892bf75b2034 ("ion: Switch ion to use dma-buf")
> > > > > > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > > > > > ---
> > > > > >  drivers/staging/android/ion/ion.c | 3 +++
> > > > > >  1 file changed, 3 insertions(+)
> > > > > > 
> > > > > > diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> > > > > > index 806e9b30b9dc8..30f359faba575 100644
> > > > > > --- a/drivers/staging/android/ion/ion.c
> > > > > > +++ b/drivers/staging/android/ion/ion.c
> > > > > > @@ -509,6 +509,9 @@ static void *ion_handle_kmap_get(struct ion_handle *handle)
> > > > > >  	void *vaddr;
> > > > > >  
> > > > > >  	if (handle->kmap_cnt) {
> > > > > > +		if (handle->kmap_cnt + 1 < handle->kmap_cnt)
> > > > > 
> > > > > What about using the nice helpers in overflow.h for this?
> > > > 
> > > > I haven't heard of these before.
> > > > 
> > > > Looks like they're not widely used.
> > > > 
> > > > I'll try them out and see how they go.
> > > > 
> > > > > > +			return ERR_PTR(-EOVERFLOW);
> > > > > > +
> > > > > >  		handle->kmap_cnt++;
> > > > > >  		return buffer->vaddr;
> > > > > >  	}
> > > > > 
> > > > > What stable kernel branch(es) is this for?
> > > > 
> > > > I assumed your magic scripts could determine this from the Fixes:
> > > > tag.  I'll be more explicit in v2.
> > > 
> > > The fixes tag says how far back for it to go, but not where to start
> > > that process from :)
> > 
> > What's your preferred method for identifying a start-point?
> > 
> > In the [PATCH] tag or appended on to Cc: stable ... # <here>?
> > 
> > I know both work, but what makes your life easier?
> 
> Easiest is below the --- line say:
> ---
>  This is for kernel versions X.X and older.

Understood, thanks.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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