linux-kernel - Re: [PATCH] media: staging: atomisp: fix a potential missing-check bug

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Message-ID: <20180508132610.4wr5vtduy4fjrqm7@kekkonen.localdomain>
Date:   Tue, 8 May 2018 16:26:10 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kangjie Lu <kjlu@....edu>,
        "open list:STAGING - ATOMISP DRIVER" <linux-media@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH] media: staging: atomisp: fix a potential missing-check
 bug

On Tue, May 08, 2018 at 08:04:54AM -0500, Wenwen Wang wrote:
> On Tue, May 8, 2018 at 7:16 AM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> > On Wed, May 02, 2018 at 05:38:49PM -0500, Wenwen Wang wrote:
> >> At the end of atomisp_subdev_set_selection(), the function
> >> atomisp_subdev_get_rect() is invoked to get the pointer to v4l2_rect. Since
> >> this function may return a NULL pointer, it is firstly invoked to check
> >> the returned pointer. If the returned pointer is not NULL, then the
> >> function is invoked again to obtain the pointer and the memory content
> >> at the location of the returned pointer is copied to the memory location of
> >> r. In most cases, the pointers returned by the two invocations are same.
> >> However, given that the pointer returned by the function
> >> atomisp_subdev_get_rect() is not a constant, it is possible that the two
> >> invocations return two different pointers. For example, another thread may
> >> race to modify the related pointers during the two invocations.
> >
> > You're assuming a very serious race condition exists.
> >
> >
> >> In that
> >> case, even if the first returned pointer is not null, the second returned
> >> pointer might be null, which will cause issues such as null pointer
> >> dereference.
> >
> > And then complaining that if a really serious bug exists then this very
> > minor bug would exist too...  If there were really a race condition like
> > that then we'd want to fix it instead.  In other words, this is not a
> > real life bug fix.
> >
> > But it would be fine as a readability or static checker fix so that's
> > fine.
> 
> Thanks for your response. From the performance perspective, this bug
> should also be fixed, as the second invocation is redundant if it is
> expected to return a same pointer as the first one.

The arguments are unchanged so the function returns the same pointer.

Btw. this driver is being removed; please see discussion here:

<URL:https://www.spinics.net/lists/linux-media/msg133223.html>

-- 
Sakari Ailus
sakari.ailus@...ux.intel.com