linux-kernel - Re: [PATCH] USB: core: Fix a NULL pointer dereference

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Date:   Thu, 14 Sep 2023 21:42:48 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Yuran Pereira <yuran.pereira@...mail.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "royluo@...gle.com" <royluo@...gle.com>,
        "christophe.jaillet@...adoo.fr" <christophe.jaillet@...adoo.fr>,
        "raychi@...gle.com" <raychi@...gle.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "syzbot+c063a4e176681d2e0380@...kaller.appspotmail.com" 
        <syzbot+c063a4e176681d2e0380@...kaller.appspotmail.com>
Subject: Re: [PATCH] USB: core: Fix a NULL pointer dereference

On Fri, Sep 15, 2023 at 12:57:58AM +0000, Yuran Pereira wrote:
> Hello Alan,
> 
> Thank you for the detailed explanation.
> 
> Apologies for the delay replying.
> Please, feel free to submit the patch.

No need; Andy Shevchenko already submitted the same patch some time ago 
and it has been merged.

Alan Stern

> ________________________________
> De: Alan Stern <stern@...land.harvard.edu>
> Enviado: 9 de setembro de 2023 14:36
> Para: Yuran Pereira <yuran.pereira@...mail.com>; Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: gregkh@...uxfoundation.org <gregkh@...uxfoundation.org>; royluo@...gle.com <royluo@...gle.com>; christophe.jaillet@...adoo.fr <christophe.jaillet@...adoo.fr>; raychi@...gle.com <raychi@...gle.com>; linux-usb@...r.kernel.org <linux-usb@...r.kernel.org>; linux-kernel@...r.kernel.org <linux-kernel@...r.kernel.org>; syzbot+c063a4e176681d2e0380@...kaller.appspotmail.com <syzbot+c063a4e176681d2e0380@...kaller.appspotmail.com>
> Assunto: Re: [PATCH] USB: core: Fix a NULL pointer dereference
> 
> On Sat, Sep 09, 2023 at 06:28:12AM +0000, Yuran Pereira wrote:
> > Hello Alan,
> >
> > Thank you for elucidating that.
> >
> > So, this bug is present on the mainline tree which is where syzkaller
> > found it. My patch was also based on the mainline tree.
> >
> > I just ran the same reproducer against a kernel compiled from the usb
> > tree, and, as you suggested, the test you mentioned does in fact,
> > prevent the bug from occurring.
> >
> > Please forgive my ignorance; I am a new contributor to the community.
> > But in this situation how should I proceed? Is there even a need to
> > submit a patch, or will the code currently present in the usb tree
> > eventually be reflected in the mainline?
> 
> The first step is to find the difference between the mainline and USB
> trees that is responsible for this change in behavior.  A quick check of
> the Git logs shows that the change was caused by commit d21fdd07cea4
> ("driver core: Return proper error code when dev_set_name() fails"),
> written by Andy Shevchenko.  As a result of this commit, the code in
> device_add() now says:
> 
>         if (dev_name(dev))
>                 error = 0;
>         /* subsystems can specify simple device enumeration */
>         else if (dev->bus && dev->bus->dev_name)
>                 error = dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id);
>         if (error)
>                 goto name_error;
> 
> This obviously omits a final "else" clause; it should say:
> 
>         if (dev_name(dev))
>                 error = 0;
>         /* subsystems can specify simple device enumeration */
>         else if (dev->bus && dev->bus->dev_name)
>                 error = dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id);
> +       else
> +               error = -EINVAL;
>         if (error)
>                 goto name_error;
> 
> So to answer your questions: No, the code in the USB tree will not find
> its way into mainline.  The opposite will happen: The mainline code will
> land in the USB tree.  Which means that yes, there is a need to submit a
> patch.  You can go ahead and write this up for submission, or I can
> submit it for you.  Or you can check with Andy and see if he wants to
> fix the problem in a different way.
> 
> Alan Stern