Fix UVC gadget support on 32-bit systems

[w23]

Note that this is clearly a common upstream problem, not specific to Raspberry Pi. I will work with mainline kernel to get this upstreamed (when I figure out how to do so :)), which will take quite some time.

Given that currently UVC gadget support is completely broken on 6.6 32-bit kernel, I believe that this is valuable for the community to be included into Raspberry Pi kernels sooner than doing it in the roundabout way through upstream.

The problem description follows:

Commit 0df2860 introduced a helper function to parse commonly occurring strings containing lists of numbers. Original functions used buf buffer on stack, and queried its size using sizeof(buf) to avoid overrun. The newly intruduced function, however, used a dynamically sized heap-allocated buffer, but wasn't updated to use this new buffer size instead of just sizeof.

Therefore, parsing now can only read items of size 3 max on 32-bit systems, and of size 7 on 64-bit ones. Some UVC fields do need numbers with more digits, e.g. dwFrameInteval needs at least 5-6, so it fails to be written into, thus completely breaking UVC gadget support on 32 bit systems.

[pelwell]

GregKH is a very busy man, and moving the code obscured the changes, but that's still really bad. I expect your patch (https://lore.kernel.org/lkml/[email protected]/raw) to be welcomed upstream with open arms - isn't that right, @pinchartl?

Can I append your S-o-b (Signed-off-by: Ivan Avdeev <[email protected]>) when I merge?

[w23]

Can I append your S-o-b (Signed-off-by: Ivan Avdeev <[email protected]>) when I merge?

Absolutely!
It would probably make sense to just copy the whole patch description that I sent to the mainline instead of this description when merging. I made this PR a few days before I had a chance to read on how to make kernel patches probably, so it's not really compliant :).

[pelwell]

Superseded by 1dc282d.