[PATCH] dma-buf: return -EINVAL if dmabuf object is NULL

[Sa, Nuno]

> From: Christian König <christian.koenig at amd.com>
> Sent: Wednesday, August 18, 2021 2:10 PM
> To: Sa, Nuno <Nuno.Sa at analog.com>; linaro-mm-sig at lists.linaro.org;
> dri-devel at lists.freedesktop.org; linux-media at vger.kernel.org
> Cc: Rob Clark <rob at ti.com>; Sumit Semwal
> <sumit.semwal at linaro.org>
> Subject: Re: [PATCH] dma-buf: return -EINVAL if dmabuf object is
> NULL
> 
> [External]
> 
> To be honest I think the if(WARN_ON(!dmabuf)) return -EINVAL
> handling
> here is misleading in the first place.
> 
> Returning -EINVAL on a hard coding error is not good practice and
> should
> probably be removed from the DMA-buf subsystem in general.

Would you say to just return 0 then? I don't think that having the
dereference is also good..

I used -EINVAL to be coherent with the rest of the code.

- Nuno Sá

> Christian.
> 
> Am 18.08.21 um 13:58 schrieb Nuno Sá:
> > On top of warning about a NULL object, we also want to return with a
> > proper error code (as done in 'dma_buf_begin_cpu_access()').
> Otherwise,
> > we will get a NULL pointer dereference.
> >
> > Fixes: fc13020e086b ("dma-buf: add support for kernel cpu access")
> > Signed-off-by: Nuno Sá <nuno.sa at analog.com>
> > ---
> >   drivers/dma-buf/dma-buf.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-
> buf.c
> > index 63d32261b63f..8ec7876dd523 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -1231,7 +1231,8 @@ int dma_buf_end_cpu_access(struct
> dma_buf *dmabuf,
> >   {
> >   	int ret = 0;
> >
> > -	WARN_ON(!dmabuf);
> > +	if (WARN_ON(!dmabuf))
> > +		return -EINVAL;
> >
> >   	might_lock(&dmabuf->resv->lock.base);
> >