linux-kernel - Re: Safety of opening up /dev/dma_heap/* to physically present users (udev uaccess tag) ?

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Message-ID: <4f59a9d78662831123cc7e560218fa422e1c5eca.camel@collabora.com>
Date: Tue, 07 May 2024 16:07:39 -0400
From: Nicolas Dufresne <nicolas.dufresne@...labora.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, Daniel Vetter
	 <daniel@...ll.ch>
Cc: Bryan O'Donoghue <bryan.odonoghue@...aro.org>, Dmitry Baryshkov
 <dmitry.baryshkov@...aro.org>, Hans de Goede <hdegoede@...hat.com>, Sumit
 Semwal <sumit.semwal@...aro.org>, Benjamin Gaignard
 <benjamin.gaignard@...labora.com>, Brian Starkey <Brian.Starkey@....com>,
 John Stultz <jstultz@...gle.com>, "T.J. Mercier" <tjmercier@...gle.com>,
 Christian König <christian.koenig@....com>, Lennart
 Poettering <mzxreary@...inter.de>,  Robert Mader
 <robert.mader@...labora.com>, Sebastien Bacher
 <sebastien.bacher@...onical.com>, Linux Media Mailing List
 <linux-media@...r.kernel.org>, "dri-devel@...ts.freedesktop.org"
 <dri-devel@...ts.freedesktop.org>,  linaro-mm-sig@...ts.linaro.org, Linux
 Kernel Mailing List <linux-kernel@...r.kernel.org>, Milan Zamazal
 <mzamazal@...hat.com>, Maxime Ripard <mripard@...hat.com>, Andrey Konovalov
 <andrey.konovalov.ynk@...il.com>
Subject: Re: Safety of opening up /dev/dma_heap/* to physically present
 users (udev uaccess tag) ?

Hi,

Le mardi 07 mai 2024 à 21:36 +0300, Laurent Pinchart a écrit :
> Shorter term, we have a problem to solve, and the best option we have
> found so far is to rely on dma-buf heaps as a backend for the frame
> buffer allocatro helper in libcamera for the use case described above.
> This won't work in 100% of the cases, clearly. It's a stop-gap measure
> until we can do better.

Considering the security concerned raised on this thread with dmabuf heap
allocation not be restricted by quotas, you'd get what you want quickly with
memfd + udmabuf instead (which is accounted already).

It was raised that distro don't enable udmabuf, but as stated there by Hans, in
any cases distro needs to take action to make the softISP works. This
alternative is easy and does not interfere in anyway with your future plan or
the libcamera API. You could even have both dmabuf heap (for Raspbian) and the
safer memfd+udmabuf for the distro with security concerns.

And for the long term plan, we can certainly get closer by fixing that issue
with accounting. This issue also applied to v4l2 io-ops, so it would be nice to
find common set of helpers to fix these exporters.

regards,
Nicolas