linux-kernel - Re: [PATCH][next] wifi: rtl8xxxu: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <f6f7cca3-0de8-4b97-9b8c-b76ba2561f0e@gmail.com>
Date: Mon, 8 Dec 2025 02:05:19 +0200
From: Bitterblue Smith <rtl8821cerfe2@...il.com>
To: Michal Pecio <michal.pecio@...il.com>
Cc: Ping-Ke Shih <pkshih@...ltek.com>, Zenm Chen <zenmchen@...il.com>,
 "gustavo@...eddedor.com" <gustavo@...eddedor.com>,
 "Jes.Sorensen@...il.com" <Jes.Sorensen@...il.com>,
 "gustavoars@...nel.org" <gustavoars@...nel.org>,
 "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
 linux-usb@...r.kernel.org
Subject: Re: [PATCH][next] wifi: rtl8xxxu: Avoid
 -Wflex-array-member-not-at-end warnings

On 07/12/2025 01:16, Michal Pecio wrote:
> Hi,
> 
>>>> I got something. In my case everything seemed fine until I
>>>> unplugged the wifi adapter. And then the system still worked for a
>>>> few minutes before it froze.
> 
> Sounds like memory corruption.
> 
>>> Zenm and I tested below changes which can also reproduce the
>>> symptom, so I wonder driver might assume urb is the first member of
>>> struct, but unfortunately I can't find that.
> 
> That's what it seems to be doing, because it uses usb_init_urb()
> on urbs embedded in some struct and then usb_free_urb().
> 
> If you look what usb_free_urb() does, it decrements refcount and
> attempts to free urb. But here urb is a member of a larger struct,
> so I guess the whole struct is freed (and this was either intentional
> or a bug that didn't happen to blow up yet).
> 
> Now a bogus address is being passed to kfree() and things go boom.
> Or at least that's my first guess after spending a few minutes.
> But that's the direction I would be looking at.
> 
> Regards,
> Michal

Ahhh, I see it now, thank you.