HID: pidff: Fix null pointer dereference in pidff_find_fields

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>

Author: Lawstorant

drivers/hid/usbhid/hid-pidff.c

@@ -926,6 +926,11 @@ static void pidff_set_autocenter(struct input_dev *dev, u16 magnitude)
 static int pidff_find_fields(struct pidff_usage *usage, const u8 *table,
 			     struct hid_report *report, int count, int strict)
 {
+	if (!report) {
+		pr_debug("pidff_find_fields, null report\n");
+		return -1;
+	}
+
 	int i, j, k, found;
 	int return_value = 0;
 
@@ -1050,6 +1055,11 @@ static int pidff_reports_ok(struct pidff_device *pidff)
 static struct hid_field *pidff_find_special_field(struct hid_report *report,
 						  int usage, int enforce_min)
 {
+	if (!report) {
+		pr_debug("pidff_find_special_field, null report\n");
+		return NULL;
+	}
+
 	int i;
 
 	for (i = 0; i < report->maxfield; i++) {