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

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Date: Tue, 4 Jun 2024 16:15:18 +0200 (CEST)
From: Jiri Kosina <jikos@...nel.org>
To: Kees Cook <kees@...nel.org>
cc: Nikita Zhandarovich <n.zhandarovich@...tech.ru>, 
    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()

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?

-- 
Jiri Kosina
SUSE Labs