Hi, On Mon, May 06, 2024 at 01:49:17PM GMT, Hans de Goede wrote: > Hi dma-buf maintainers, et.al., > > Various people have been working on making complex/MIPI cameras work OOTB > with mainline Linux kernels and an opensource userspace stack. > > The generic solution adds a software ISP (for Debayering and 3A) to > libcamera. Libcamera's API guarantees that buffers handed to applications > using it are dma-bufs so that these can be passed to e.g. a video encoder. > > In order to meet this API guarantee the libcamera software ISP allocates > dma-bufs from userspace through one of the /dev/dma_heap/* heaps. For > the Fedora COPR repo for the PoC of this: > https://hansdegoede.dreamwidth.org/28153.html For the record, we're also considering using them for ARM KMS devices, so it would be better if the solution wasn't only considering v4l2 devices. > I have added a simple udev rule to give physically present users access > to the dma_heap-s: > > KERNEL=="system", SUBSYSTEM=="dma_heap", TAG+="uaccess" > > (and on Rasperry Pi devices any users in the video group get access) > > This was just a quick fix for the PoC. Now that we are ready to move out > of the PoC phase and start actually integrating this into distributions > the question becomes if this is an acceptable solution; or if we need some > other way to deal with this ? > > Specifically the question is if this will have any negative security > implications? I can certainly see this being used to do some sort of > denial of service attack on the system (1). This is especially true for > the cma heap which generally speaking is a limited resource. There's plenty of other ways to exhaust CMA, like allocating too much KMS or v4l2 buffers. I'm not sure we should consider dma-heaps differently than those if it's part of our threat model. > But devices tagged for uaccess are only opened up to users who are > physcially present behind the machine and those can just hit > the powerbutton, so I don't believe that any *on purpose* DOS is part of > the thread model. How would that work for headless devices? Maxime
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