Re: [PATCH v1] can: can327: Clean up payload encoding in can327_handle_prompt()

[Max Staudt]

On 11/20/24 02:15, Max Staudt wrote:
> A bit off-topic, but since CAN_RAW came up: Why does CAN_RAW even 
> sanitise anything at all, instead of relying on checks on later layers? 
> It seems like quite a few checks are duplicated. And all the while it's 
> possible for userspace to do weird stuff like seemingly enabling CAN FD 
> on the socket via setsockopt() CAN_RAW_FD_FRAMES, but that's only 
> flipping a bit on the CAN_RAW socket, yet changes nothing underneath. It 
> was quite confusing to read. I suppose the explanation is "legacy"?

Answering my own question here:

CAN_RAW_FD_FRAMES modifies what frames are allowed to pass through the 
CAN_RAW socket towards userspace. This way, simple software handling 
only CAN 2.0 frames may assume that reading anything other than CAN_MTU 
bytes from the socket is an error. This keeps the code simple, and old 
programs have to be written this way, because there is no way for them 
to guess what not yet implemented CAN versions will look like.

So, this option makes a lot more sense to me now, sorry for the extra 
noise :)


Max