linux-kernel - Re: [PATCH] HID: usbhid: fix recurrent out-of-bounds bug in usbhid

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Message-ID: <2a38e355-af5c-4b3d-81be-0cc97376c1f5@fintech.ru>
Date: Tue, 4 Jun 2024 10:09:43 -0700
From: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
To: Jiri Kosina <jikos@...nel.org>, Kees Cook <kees@...nel.org>
CC: Benjamin Tissoires <bentiss@...nel.org>, Kees Cook
	<keescook@...omium.org>, <linux-usb@...r.kernel.org>,
	<linux-input@...r.kernel.org>, <syzkaller-bugs@...glegroups.com>,
	<linux-kernel@...r.kernel.org>,
	<syzbot+c52569baf0c843f35495@...kaller.appspotmail.com>,
	<linux-hardening@...r.kernel.org>
Subject: Re: [PATCH] HID: usbhid: fix recurrent out-of-bounds bug in
 usbhid_parse()

Hi,

On 6/4/24 07:15, Jiri Kosina wrote:
> On Tue, 4 Jun 2024, Kees Cook wrote:
> 
>> 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.
> 
> Ah, you are of course right, not sure what I was thinking. Thanks a lot 
> for catching my brainfart.
> 
> I am dropping the patch for now; Nikita, will you please send a refreshed 
> one?
> 

Thanks for catching my mistake.

I'll gladly send a revised version, hoping to do it very soon.

Regards,
Nikita