Re: [PATCH] HID: usbhid: fix recurrent out-of-bounds bug in usbhid_parse()

[Kees Cook]

On June 4, 2024 1:15:35 AM PDT, Jiri Kosina <jikos@xxxxxxxxxx> wrote:
>On Fri, 24 May 2024, Nikita Zhandarovich wrote:
>
>> Syzbot reports [1] a reemerging out-of-bounds bug regarding hid
>> descriptors possibly having incorrect bNumDescriptors values in
>> usbhid_parse().
>> 
>> Build on the previous fix in "HID: usbhid: fix out-of-bounds bug"
>> and run a sanity-check ensuring that number of descriptors doesn't
>> exceed the size of desc[] in struct hid_descriptor.
>> 
>> [1] Syzbot report:
>> Link: https://syzkaller.appspot.com/bug?extid=c52569baf0c843f35495
>> 
>> UBSAN: array-index-out-of-bounds in drivers/hid/usbhid/hid-core.c:1024:7
>> index 1 is out of range for type 'struct hid_class_descriptor[1]'
>> CPU: 0 PID: 8 Comm: kworker/0:1 Not tainted 6.9.0-rc6-syzkaller-00290-gb9158815de52 #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
>> Workqueue: usb_hub_wq hub_event
>> Call Trace:
>>  <TASK>
>>  __dump_stack lib/dump_stack.c:88 [inline]
>>  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
>>  ubsan_epilogue lib/ubsan.c:231 [inline]
>>  __ubsan_handle_out_of_bounds+0x121/0x150 lib/ubsan.c:429
>>  usbhid_parse+0x5a7/0xc80 drivers/hid/usbhid/hid-core.c:1024
>>  hid_add_device+0x132/0x520 drivers/hid/hid-core.c:2790
>>  usbhid_probe+0xb38/0xea0 drivers/hid/usbhid/hid-core.c:1429
>>  usb_probe_interface+0x645/0xbb0 drivers/usb/core/driver.c:399
>>  really_probe+0x2b8/0xad0 drivers/base/dd.c:656
>>  __driver_probe_device+0x1a2/0x390 drivers/base/dd.c:798
>>  driver_probe_device+0x50/0x430 drivers/base/dd.c:828
>>  __device_attach_driver+0x2d6/0x530 drivers/base/dd.c:956
>>  bus_for_each_drv+0x24e/0x2e0 drivers/base/bus.c:457
>>  __device_attach+0x333/0x520 drivers/base/dd.c:1028
>>  bus_probe_device+0x189/0x260 drivers/base/bus.c:532
>>  device_add+0x8ff/0xca0 drivers/base/core.c:3720
>>  usb_set_configuration+0x1976/0x1fb0 drivers/usb/core/message.c:2210
>>  usb_generic_driver_probe+0x88/0x140 drivers/usb/core/generic.c:254
>>  usb_probe_device+0x1b8/0x380 drivers/usb/core/driver.c:294
>> 
>> Reported-and-tested-by: syzbot+c52569baf0c843f35495@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Fixes: f043bfc98c19 ("HID: usbhid: fix out-of-bounds bug")
>> Signed-off-by: Nikita Zhandarovich <n.zhandarovich@xxxxxxxxxx>
>
>Applied, thanks.

This isn't the right solution. The problem is that hid_class_descriptor is a flexible array but was sized as a single element fake flexible array: 

struct hid_descriptor {
	   __u8  bLength;
	   __u8  bDescriptorType;
	   __le16 bcdHID;
	   __u8  bCountryCode;
	   __u8  bNumDescriptors;

	   struct hid_class_descriptor desc[1];
} __attribute__ ((packed));

This likely needs to be: 

struct hid_class_descriptor desc[] __counted_by(bNumDescriptors);

And then check for any sizeof() uses of the struct that might have changed.



-- 
Kees Cook