linux-kernel - Re: [PATCH] sh: mm: Fix unprotected access to struct device

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Date:   Wed, 18 Apr 2018 15:13:14 +0200
From:   jacopo mondi <jacopo@...ndi.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        ysato@...rs.sourceforge.jp, dalias@...c.org,
        thomas.petazzoni@...e-electrons.com, robin.murphy@....com,
        geert@...ux-m68k.org, linux-renesas-soc@...r.kernel.org,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sh: mm: Fix unprotected access to struct device

Hi Christoph,

On Wed, Apr 18, 2018 at 03:47:03AM -0700, Christoph Hellwig wrote:
> On Tue, Apr 17, 2018 at 03:35:23PM +0200, Jacopo Mondi wrote:
> > With commit ce88313069c36eef80f21fd7 ("arch/sh: make the DMA mapping
> > operations observe dev->dma_pfn_offset") the generic DMA allocation
> > function on which the SH 'dma_alloc_coherent()' function relies on,
> > access the 'dma_pfn_offset' field of struct device.
> >
> > Unfortunately the 'dma_generic_alloc_coherent()' function is called from
> > several places with a NULL struct device argument, halting the CPU
> > during the boot process.
> >
> > This patch fixes the issue protecting access to dev->dma_pfn_offset,
> > with a trivial check for validity. It also passes a valid 'struct device'
> > in the 'platform_resource_setup_memory' function which is the main user
> > of 'dma_alloc_coherent()', and inserting a WARN_ON() check to make future
> > (and existing) bogus users of this function they're should provide a valid
> > 'struct device' whenever possible.
>
> Please fix those callers to not pass a NULL pointer instead.

As long as it goes for arch/sh, the only user of dma_alloc_coherent()
is platform_resource_setup_memory(), and it has been fixed by this
patch.

Unfortunately, as Thomas pointed out, there are drivers which calls
into this with the wrong 'struct device' as the sh_eth one he had fixed.

I would then say that as long as it goes for the NULL case, we should be
fine now.

Thanks
   j

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