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

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Date:   Tue, 14 Dec 2021 14:32:04 +0100
From:   Mauro Carvalho Chehab <mchehab@...nel.org>
To:     Dongliang Mu <mudongliangabcd@...il.com>
Cc:     Antti Palosaari <crope@....fi>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: msi2500: fix UAF in the msi2500_disconnect

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_*?

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