HID: bpf: prevent infinite recursions with hid_hw_raw_requests hooks

When we attach a sleepable hook to hid_hw_raw_requests, we can (and in
many cases should) call ourself hid_bpf_raw_request(), to actually fetch
data from the device itself.

However, this means that we might enter an infinite loop between
hid_hw_raw_requests hooks and hid_bpf_hw_request() call.

To prevent that, if a hid_bpf_hw_request() call is emitted, we prevent
any new call of this kfunc by storing the information in the context.
This way we can always trace/monitor/filter the incoming bpf requests,
while preventing those loops to happen.

I don't think exposing "from_bpf" is very interesting because while
writing such a bpf program, you need to match at least the report number
and/or the source of the call. So a blind "if there is a
hid_hw_raw_request() call, I'm emitting another one" makes no real
sense.

Link: https://patch.msgid.link/20240626-hid_hw_req_bpf-v2-5-cfd60fb6c79f@kernel.org


Acked-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>