usb/media/imon: null-ptr-deref in imon_probe

[Andrey Konovalov]

Hi!

I've got the following report while fuzzing the kernel with syzkaller.

On commit 8a5776a5f49812d29fe4b2d0a2d71675c3facf3f (4.14-rc4).

It seems that the return value of usb_ifnum_to_if() can be NULL and
needs to be checked.

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
Modules linked in:
CPU: 1 PID: 1497 Comm: kworker/1:1 Not tainted
4.14.0-rc4-43418-g43a3f84d2109-dirty #380
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: usb_hub_wq hub_event
task: ffff88006a5618c0 task.stack: ffff880068bc8000
RIP: 0010:imon_probe+0x231/0x3f10 drivers/media/rc/imon.c:2519
RSP: 0018:ffff880068bce2d8 EFLAGS: 00010206
RAX: 0000000000000000 RBX: ffff8800627dd500 RCX: 0000000000000027
RDX: dffffc0000000000 RSI: 0000000000000000 RDI: 0000000000000138
RBP: ffff880068bce5e8 R08: ffff88006a5618c0 R09: ffffffff84b380fc
R10: ffff880068bce2c8 R11: 1ffff1000d4ac5b3 R12: ffff880061830000
R13: ffff880061830008 R14: ffffffff883fa200 R15: ffffffff883fa080
FS:  0000000000000000(0000) GS:ffff88006c500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000206cbffc CR3: 0000000061085000 CR4: 00000000000006e0
Call Trace:
 usb_probe_interface+0x35d/0x8e0 drivers/usb/core/driver.c:361
 really_probe drivers/base/dd.c:413
 driver_probe_device+0x610/0xa00 drivers/base/dd.c:557
 __device_attach_driver+0x230/0x290 drivers/base/dd.c:653
 bus_for_each_drv+0x161/0x210 drivers/base/bus.c:463
 __device_attach+0x26e/0x3d0 drivers/base/dd.c:710
 device_initial_probe+0x1f/0x30 drivers/base/dd.c:757
 bus_probe_device+0x1eb/0x290 drivers/base/bus.c:523
 device_add+0xd0b/0x1660 drivers/base/core.c:1835
 usb_set_configuration+0x104e/0x1870 drivers/usb/core/message.c:1932
 generic_probe+0x73/0xe0 drivers/usb/core/generic.c:174
 usb_probe_device+0xaf/0xe0 drivers/usb/core/driver.c:266
 really_probe drivers/base/dd.c:413
 driver_probe_device+0x610/0xa00 drivers/base/dd.c:557
 __device_attach_driver+0x230/0x290 drivers/base/dd.c:653
 bus_for_each_drv+0x161/0x210 drivers/base/bus.c:463
 __device_attach+0x26e/0x3d0 drivers/base/dd.c:710
 device_initial_probe+0x1f/0x30 drivers/base/dd.c:757
 bus_probe_device+0x1eb/0x290 drivers/base/bus.c:523
 device_add+0xd0b/0x1660 drivers/base/core.c:1835
 usb_new_device+0x7b8/0x1020 drivers/usb/core/hub.c:2457
 hub_port_connect drivers/usb/core/hub.c:4903
 hub_port_connect_change drivers/usb/core/hub.c:5009
 port_event drivers/usb/core/hub.c:5115
 hub_event+0x194d/0x3740 drivers/usb/core/hub.c:5195
 process_one_work+0xc7f/0x1db0 kernel/workqueue.c:2119
 worker_thread+0x221/0x1850 kernel/workqueue.c:2253
 kthread+0x3a1/0x470 kernel/kthread.c:231
 ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
Code: ff e8 a4 81 cb 01 31 f6 48 89 df e8 2a cc 65 ff 0f ae f0 48 8d
b8 38 01 00 00 48 ba 00 00 00 00 00 fc ff df 48 89 f9 48 c1 e9 03 <80>
3c 11 00 0f 85 e8 31 00 00 48 8b 98 38 01 00 00 0f ae f0 44
RIP: imon_probe+0x231/0x3f10 RSP: ffff880068bce2d8
---[ end trace 07febd2eebe02f84 ]---