linux-kernel - RE: [PATCH v4.19.x] make 'user_access_begin()' do 'access

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Message-ID: <MN2PR05MB63814CDAAF6828285929736ACDBF0@MN2PR05MB6381.namprd05.prod.outlook.com>
Date:   Wed, 13 May 2020 17:08:19 +0000
From:   Ashwin H <ashwinh@...are.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...nel.org" <stable@...nel.org>,
        Srivatsa Bhat <srivatsab@...are.com>,
        "srivatsa@...il.mit.edu" <srivatsa@...il.mit.edu>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        Steven Rostedt <srostedt@...are.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: RE: [PATCH v4.19.x] make 'user_access_begin()' do 'access_ok()'

> Ok, but what does that mean for us?
> 
> You need to say why you are sending a patch, otherwise we will guess wrong.

In drivers/gpu/drm/i915/i915_gem_execbuffer.c, ioctl functions does user_access_begin() without doing access_ok(Checks if a user space pointer is valid)  first.
A local attacker can craft a malicious ioctl function call to overwrite arbitrary kernel memory, resulting in a Denial of Service or privilege escalation (CVE-2018-20669)

This patch makes sure that user_access_begin always does access_ok. 
user_access_begin has been modified to do access_ok internally.

Thanks,
Ashwin