linux-kernel - Re: [PATCH] dma-mapping: remove an unnecessary NULL check

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Date:   Wed, 24 Apr 2019 16:27:43 +0200
From:   Christoph Hellwig <hch@....de>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Christoph Hellwig <hch@....de>, Ian Abbott <abbotti@....co.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org,
        "kernel-janitors@...r.kernel.org H Hartley Sweeten" 
        <hsweeten@...ionengravers.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-mapping: remove an unnecessary NULL check

On Wed, Apr 24, 2019 at 05:24:37PM +0300, Dan Carpenter wrote:
> We already dereferenced "dev" when we called get_dma_ops() so this NULL
> check is too late.  We're not supposed to pass NULL "dev" pointers to
> dma_alloc_attrs().

Thanks, applied to the dma-mapping for-next tree.

> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> There are still at least two drivers which do pass a NULL unfortunately.
> 
> drivers/staging/comedi/drivers/comedi_isadma.c:195 comedi_isadma_alloc() error: NULL dereference inside function 'dma_alloc_coherent()'
> drivers/staging/comedi/drivers/comedi_isadma.c:227 comedi_isadma_free() error: NULL dereference inside function 'dma_free_coherent()'

This is staging code.  Per official decree from Linus we can just
ignore it, and I tend to do so to keep my sanity.

> drivers/tty/synclink.c:3667 mgsl_alloc_buffer_list_memory() error: NULL dereference inside function 'dma_alloc_coherent()'
> drivers/tty/synclink.c:3738 mgsl_free_buffer_list_memory() error: NULL dereference inside function 'dma_free_coherent()'
> drivers/tty/synclink.c:3777 mgsl_alloc_frame_memory() error: NULL dereference inside function 'dma_alloc_coherent()'
> drivers/tty/synclink.c:3811 mgsl_free_frame_memory() error: NULL dereference inside function 'dma_free_coherent()'

The !PCI case there is dead since I removed PCI support a while ago.
Looks like it is still too convoluted for static checkers to notice that,
though.