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

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Message-ID: <20180508121635.mdw4jikv66iyprie@mwanda>
Date:   Tue, 8 May 2018 15:16:35 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Wenwen Wang <wang6495@....edu>
Cc:     "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>,
        Sakari Ailus <sakari.ailus@...ux.intel.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 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.

regards,
dan carpenter