linux-kernel - Re: [PATCH 4.19 124/125] HID: hiddev: Fix slab-out-of-bounds write in hiddev_ioctl

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Date:   Tue, 1 Sep 2020 22:36:28 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+34ee1b45d88571c2fa8b@...kaller.appspotmail.com,
        Peilin Ye <yepeilin.cs@...il.com>,
        Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 4.19 124/125] HID: hiddev: Fix slab-out-of-bounds write
 in hiddev_ioctl_usage()

On Tue, Sep 01, 2020 at 09:12:09PM +0200, Pavel Machek wrote:
> Hi!
> 
> > commit 25a097f5204675550afb879ee18238ca917cba7a upstream.
> > 
> > `uref->usage_index` is not always being properly checked, causing
> > hiddev_ioctl_usage() to go out of bounds under some cases. Fix it.
> 
> Well, the code is quite confusig, but:
> 
> a) does HIDIOCGCOLLECTIONINDEX need same checking?

It's checked in the previous switch statement.

> 
> b) should we check this using some kind of _nospec() variant to
> prevent speculation attacks?

I don't think so.  I wrote up an explanation earlier just because the
code was so confusing.

https://lkml.org/lkml/2020/7/20/523

regards,
dan carpenter