HID: bpf: remove double fdget()

HID: bpf: remove double fdget()

commit 7cdd2108903a4e369eb37579830afc12a6877ec2 upstream.

When the kfunc hid_bpf_attach_prog() is called, we called twice fdget():
one for fetching the type of the bpf program, and one for actually
attaching the program to the device.

The problem is that between those two calls, we have no guarantees that
the prog_fd is still the same file descriptor for the given program.

Solve this by calling bpf_prog_get() earlier, and use this to fetch the
program type.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/bpf/CAO-hwJJ8vh8JD3-P43L-_CLNmPx0hWj44aom0O838vfP4=_1CA@mail.gmail.com/T/#t
Cc: <stable@vger.kernel.org>
Fixes: f5c27da4e3c8 ("HID: initial BPF implementation")
Link: https://lore.kernel.org/r/20240124-b4-hid-bpf-fixes-v2-1-052520b1e5e6@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>