HID: pidff: Fix null pointer dereference in pidff_find_fields

[ Upstream commit 22a05462c3d0eee15154faf8d13c49e6295270a5 ]

This function triggered a null pointer dereference if used to search for
a report that isn't implemented on the device. This happened both for
optional and required reports alike.

The same logic was applied to pidff_find_special_field and although
pidff_init_fields should return an error earlier if one of the required
reports is missing, future modifications could change this logic and
resurface this possible null pointer dereference again.

LKML bug report:
https://lore.kernel.org/all/CAL-gK7f5=R0nrrQdPtaZZr1fd-cdAMbDMuZ_NLA8vM0SX+nGSw@mail.gmail.com



Reported-by: Nolan Nicholson <nolananicholson@gmail.com>
Signed-off-by: Tomasz Pakuła <tomasz.pakula.oficjalny@gmail.com>
Reviewed-by: Michał Kopeć <michal@nozomi.space>
Reviewed-by: Paul Dino Jones <paul@spacefreak18.xyz>
Tested-by: Paul Dino Jones <paul@spacefreak18.xyz>
Tested-by: Cristóferson Bueno <cbueno81@gmail.com>
Tested-by: Pablo Cisneros <patchkez@protonmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>