linux-kernel - RE: [media] videobuf-dma-contig: fix vm_iomap

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Message-ID: <01a501cf4aa7$08664e30$1932ea90$@gmail.com>
Date:	Sat, 29 Mar 2014 00:58:58 +0800
From:	"Ma Haijun" <mahaijuns@...il.com>
To:	"'Hans Verkuil'" <hverkuil@...all.nl>,
	<linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Cc:	"'Mauro Carvalho Chehab'" <m.chehab@...sung.com>,
	"'Al Viro'" <viro@...IV.linux.org.uk>
Subject: RE: [media] videobuf-dma-contig: fix vm_iomap_memory() call

Hi,

> -----Original Message-----
> 
> On 03/27/2014 12:07 PM, Ma Haijun wrote:
> > Hi all,
> >
> > This is a trivial fix, but I think the patch itself has problem too.
> > The function requires a phys_addr_t, but we feed it with a dma_handle_t.
> > AFAIK, this implicit conversion does not always work.
> > Can I use virt_to_phys(mem->vaddr) to get the physical address instead?
> > (mem->vaddr and mem->dma_handle are from dma_alloc_coherent)
> 
> Does this actually fail? With what driver and on what hardware?

I notice it when I am reading the code,
so I do not know if any driver is broken.

> 
> I ask because I am very reluctant to make any changes to videobuf. It is
> slowly being replaced by the vastly superior videobuf2 framework. Existing
> drivers in the kernel still using the old videobuf seem to work just fine
> (or at least as fine as videobuf allows you to be).

Sorry that the cover letter is a bit misleading, hope you does not skip the
patch due to this.

The actual problem is that userland virtual address is erroneously passed to
vm_iomap_memory, while it expects physical address.
And that is what the patch try to address.

Seems this bug can be exploited to map and access physical address.
So it is also a security problem, I think we should ether fix it
or remove the code if not used any more.

Regards,

	Haijun


> 
> Regards,
> 
> 	Hans
> 
> >
> > Regards
> >
> > Ma Haijun
> >
> > Ma Haijun (1):
> >   [media] videobuf-dma-contig: fix incorrect argument to
> >     vm_iomap_memory() call
> >
> >  drivers/media/v4l2-core/videobuf-dma-contig.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >

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