linux-kernel - Re: [PATCH] media: msi2500: fix UAF in the msi2500

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Date:   Thu, 16 Dec 2021 09:56:13 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Antti Palosaari <crope@....fi>, linux-media@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: msi2500: fix UAF in the msi2500_disconnect

On Tue, Dec 14, 2021 at 9:32 PM Mauro Carvalho Chehab
<mchehab@...nel.org> wrote:
>
> Em Wed, 17 Nov 2021 00:32:07 +0800
> Dongliang Mu <mudongliangabcd@...il.com> escreveu:
>
> > In msi2500_probe, it invokes spi_alloc_master to allocate master
> > controller and spi_register_master to register master controller.
> > Then in msi2500_disconnect, it calls spi_unregister_master to unregister
> > the master controller. And in spi_unregister_master, it calls put_device
> > to decrease the refcount and the device object will be freed then. As a
> > result, the dereference of dev->lock will cause a use-after-free bug.
> >
> > Fix it by changing spi_alloc_master to devm_spi_alloc_master, and
> > removing spi_master_put in the error handling code.
> >
> > Note that this patch can prevent UAF occurring any more
> >
> > Fixes: fd8b5f502929 ("msi2500: move msi3101 out of staging and rename")
> > Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> > ---
> >  drivers/media/usb/msi2500/msi2500.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/media/usb/msi2500/msi2500.c b/drivers/media/usb/msi2500/msi2500.c
> > index 71de6b4c4e4c..64c3ec9f1d0c 100644
> > --- a/drivers/media/usb/msi2500/msi2500.c
> > +++ b/drivers/media/usb/msi2500/msi2500.c
> > @@ -1220,7 +1220,7 @@ static int msi2500_probe(struct usb_interface *intf,
> >       }
> >
> >       /* SPI master adapter */
> > -     master = spi_alloc_master(dev->dev, 0);
> > +     master = devm_spi_alloc_master(dev->dev, 0);
>
> We had some bad past experiences on using devm_* on USB media devices,
> as there are almost always multiple drivers loaded and multiple
> interfaces.
>
> Could you please fix the free logic instead of using devm_*?

Hi Mauro,

When I resume working on this patch, I found this UAF bug is already
fixed in the spi part and merged to the upstream.

The correct fix is spi: fix use-after-free of the add_lock mutex [1].
So let's forget this patch.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6c53b45c71b4920b5e62f0ea8079a1da382b9434


>
> Regards,
> Mauro
>
> >       if (master == NULL) {
> >               ret = -ENOMEM;
> >               goto err_unregister_v4l2_dev;
> > @@ -1233,7 +1233,6 @@ static int msi2500_probe(struct usb_interface *intf,
> >       spi_master_set_devdata(master, dev);
> >       ret = spi_register_master(master);
> >       if (ret) {
> > -             spi_master_put(master);
> >               goto err_unregister_v4l2_dev;
> >       }
> >
>
>
>
> Thanks,
> Mauro