linux-kernel - Re: [PATCH] usb: asix: Fix uninit-value in asix_mdio

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Date:   Thu, 07 Nov 2019 15:21:18 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     tranmanphong@...il.com
Cc:     syzbot+7dc7c28d4577bbe55b10@...kaller.appspotmail.com,
        gregkh@...uxfoundation.org, glider@...gle.com,
        hslester96@...il.com, kstewart@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de, linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] usb: asix: Fix uninit-value in asix_mdio_write

From: Phong Tran <tranmanphong@...il.com>
Date: Thu,  7 Nov 2019 07:44:04 +0700

> The local variables use without initilization value.
> This fixes the syzbot report.
> 
> Reported-by: syzbot+7dc7c28d4577bbe55b10@...kaller.appspotmail.com
> 
> Test result:
> 
> https://groups.google.com/d/msg/syzkaller-bugs/3H_n05x_sPU/sUoHhxgAAgAJ
> 
> Signed-off-by: Phong Tran <tranmanphong@...il.com>

There are several more situations in this file where the data blob passed
to asix_read_cmd() is read without pre-initialization not checking the
return value from asix_read_cmd().

So, syzbot can see some of them but not all of them, yet all of them
are buggy and should be fixed.

These kinds of patches drive me absolutely crazy :-)

Really, one of two things needs to happen, either asix_read_cmd() clears
the incoming buffer unconditionally, or these call sites strictly must
check the return value always before accessing the buffer after the call.

I'm not applying this, sorry.