On Tue, 3 Sep 2019, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: eea39f24 usb-fuzzer: main usb gadget fuzzer driver > git tree: https://github.com/google/kasan.git usb-fuzzer > console output: https://syzkaller.appspot.com/x/log.txt?x=14c3589e600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=d0c62209eedfd54e > dashboard link: https://syzkaller.appspot.com/bug?extid=1088533649dafa1c9004 > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1667cc66600000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10f30dbc600000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+1088533649dafa1c9...@syzkaller.appspotmail.com > > prodikeys 0003:041E:2801.0001: unknown main item tag 0x0 > prodikeys 0003:041E:2801.0001: unknown main item tag 0x0 > prodikeys 0003:041E:2801.0001: hidraw0: USB HID v0.00 Device [HID > 041e:2801] on usb-dummy_hcd.0-1/input1 > 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
The reason for this bug seems pretty clear: pcmidi_get_output_report() can return an error, but pcmidi_set_operational() doesn't bother to check the return code. Alan Stern #syz test: https://github.com/google/kasan.git eea39f24 Index: usb-devel/drivers/hid/hid-prodikeys.c =================================================================== --- usb-devel.orig/drivers/hid/hid-prodikeys.c +++ usb-devel/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 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);
