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

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Message-ID: <20251207001608.1f6940bf.michal.pecio@gmail.com>
Date: Sun, 7 Dec 2025 00:16:08 +0100
From: Michal Pecio <michal.pecio@...il.com>
To: Bitterblue Smith <rtl8821cerfe2@...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

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