linux-kernel - Re: [PATCH] omap_vout: find_vma() needs ->mmap

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Message-ID: <50282838.8ei2CtB7na@avalon>
Date:	Mon, 07 Jan 2013 15:06:18 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Archit Taneja <archit@...com>
Cc:	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, Prabhakar Lad <prabhakar.lad@...com>,
	Sakari Ailus <sakari.ailus@....fi>
Subject: Re: [PATCH] omap_vout: find_vma() needs ->mmap_sem held

Hi Mauro,

On Sunday 06 January 2013 11:02:25 Mauro Carvalho Chehab wrote:
> Em Sat, 15 Dec 2012 20:38:29 +0000 Al Viro escreveu:
> > On Sat, Dec 15, 2012 at 08:12:37PM +0000, Al Viro wrote:
> > > 	Walking rbtree while it's modified is a Bad Idea(tm); besides,
> > > 
> > > the result of find_vma() can be freed just as it's getting returned
> > > to caller.  Fortunately, it's easy to fix - just take ->mmap_sem a bit
> > > earlier (and don't bother with find_vma() at all if virtp >= PAGE_OFFSET
> > > -
> > > in that case we don't even look at its result).
> > 	
> > 	While we are at it, what prevents VIDIOC_PREPARE_BUF calling
> > 
> > v4l_prepare_buf() -> (e.g) vb2_ioctl_prepare_buf() -> vb2_prepare_buf() ->
> > __buf_prepare() -> __qbuf_userptr() -> vb2_vmalloc_get_userptr() ->
> > find_vma(), AFAICS without having taken ->mmap_sem anywhere in process? 
> > The code flow is bloody convoluted and depends on a bunch of things done
> > by initialization, so I certainly might've missed something...
> 
> This driver is currently missing an active maintainer, as it is for an old
> hardware (AFAIK, omap is now at version 4, and this is for the first one),
> but I'm c/c a few developers that might help to test and analyze it.
> 
> In any case, /me is assuming that your patch is right (as nobody
> complained), and I'm applying it right now on my tree. This will hopefully
> allow some people to test.

Please make sure you apply v2 (posted as "Re: [PATCH] omap_vout: find_vma() 
needs ->mmap_sem held").

-- 
Regards,

Laurent Pinchart

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