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

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Message-ID: <20200527153130.GA525531@kroah.com>
Date:   Wed, 27 May 2020 17:31:30 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ashwin H <ashwinh@...are.com>
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()'

On Wed, May 13, 2020 at 05:08:19PM +0000, Ashwin H wrote:
> > 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.

I had this in the tree, but it broke the build on alpha, sh, and maybe a
few others :(

See:
	https://lore.kernel.org/r/20200527140225.GA214763@roeck-us.net
for the details.

Can you dig out all of the needed follow-on patches as well, and send
them all as a patch series for 4.19.y so that I can queue them all up at
once?

thanks,

greg k-h