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

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Date: Tue, 14 May 2024 16:52:40 -0400
From: Nicolas Dufresne <nicolas.dufresne@...labora.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Maxime Ripard <mripard@...hat.com>, 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>, 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 14 mai 2024 à 23:45 +0300, Laurent Pinchart a écrit :
> > And finally, none of this fixes the issue that the heap allocation are not being
> > accounted properly and allow of an easy memory DoS. So uaccess should be granted
> > with care, meaning that defaulting a "desktop" library to that, means it will
> > most of the time not work at all.
> 
> I think that issue should be fixed, regardless of whether or not we end
> up using dma heaps for libcamera. If we do use them, maybe there will be
> a higher incentive for somebody involved in this conversation to tackle
> that problem first :-) And maybe, as a result, the rest of the Linux
> community will consider with a more open mind usage of dma heaps on
> desktop systems.

The strict reality is that if libcamera offer no alternatives, some OS will
enable it and reduce their security. I totally agree this issue needs to be
fixed regardless of libcamera, or even dma heaps. DMABuf allocation should be
accounted and limited to quotas whether it comes from a GPU, Display, V4L2 or
other type of supported devices. I would also not recommend dropping your heap
support (or preventing it from being merged) in libcamera.

Nicolas