HID: prodikeys: Fix general protection fault during probe

The syzbot fuzzer provoked a general protection fault in the
hid-prodikeys driver:

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.3.0-rc5+ #28
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: usb_hub_wq hub_event
RIP: 0010:pcmidi_submit_output_report drivers/hid/hid-prodikeys.c:300  [inline]
RIP: 0010:pcmidi_set_operational drivers/hid/hid-prodikeys.c:558 [inline]
RIP: 0010:pcmidi_snd_initialise drivers/hid/hid-prodikeys.c:686 [inline]
RIP: 0010:pk_probe+0xb51/0xfd0 drivers/hid/hid-prodikeys.c:836
Code: 0f 85 50 04 00 00 48 8b 04 24 4c 89 7d 10 48 8b 58 08 e8 b2 53 e4 fc
48 8b 54 24 20 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c 02 00 0f
85 13 04 00 00 48 ba 00 00 00 00 00 fc ff df 49 8b

The problem is caused by the fact that pcmidi_get_output_report() will
return an error if the HID device doesn't provide the right sort of
output report, but pcmidi_set_operational() doesn't bother to check
the return code and assumes the function call always succeeds.

This patch adds the missing check and aborts the probe operation if
necessary.

Reported-and-tested-by: syzbot+1088533649dafa1c9004@syzkaller.appspotmail.com
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@vger.kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-prodikeys.c

@@ -551,10 +551,14 @@ static void pcmidi_setup_extra_keys(
 
 static int pcmidi_set_operational(struct pcmidi_snd *pm)
 {
+	int rc;
+
 	if (pm->ifnum != 1)
 		return 0; /* only set up ONCE for interace 1 */
 
-	pcmidi_get_output_report(pm);
+	rc = pcmidi_get_output_report(pm);
+	if (rc < 0)
+		return rc;
 	pcmidi_submit_output_report(pm, 0xc1);
 	return 0;
 }
@@ -683,7 +687,11 @@ static int pcmidi_snd_initialise(struct pcmidi_snd *pm)
 	spin_lock_init(&pm->rawmidi_in_lock);
 
 	init_sustain_timers(pm);
-	pcmidi_set_operational(pm);
+	err = pcmidi_set_operational(pm);
+	if (err < 0) {
+		pk_error("failed to find output report\n");
+		goto fail_register;
+	}
 
 	/* register it */
 	err = snd_card_register(card);