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Subject: Re: [PATCH] dmaengine: idxd: Fix a possible NULL pointer dereference
To:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        vkoul@kernel.org, dan.j.williams@intel.com
Cc:     dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org
References: <77f0dc4f3966591d1f0cffb614a94085f8895a85.1627560174.git.christophe.jaillet@wanadoo.fr>
From:   Dave Jiang <dave.jiang@intel.com>
Message-ID: <44c9607e-2cde-02b9-7e4e-68578a775fb3@intel.com>
Date:   Thu, 29 Jul 2021 09:12:03 -0700
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On 7/29/2021 5:04 AM, Christophe JAILLET wrote:
> 'device_driver_attach()' dereferences its first argument (i.e. 'alt_drv')
> so it must not be NULL.
> Simplify the error handling logic about NULL 'alt_drv' in order to be
> more robust and future-proof.
>
> Fixes: 568b2126466f ("dmaengine: idxd: fix uninit var for alt_drv")
> Fixes: 6e7f3ee97bbe ("dmaengine: idxd: move dsa_drv support to compatible mode")
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>


Thanks for the cleanup.

Acked-by: Dave Jiang <dave.jiang@intel.com>

> ---
>   drivers/dma/idxd/compat.c | 15 ++++-----------
>   1 file changed, 4 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/dma/idxd/compat.c b/drivers/dma/idxd/compat.c
> index d7616c240dcd..3df21615f888 100644
> --- a/drivers/dma/idxd/compat.c
> +++ b/drivers/dma/idxd/compat.c
> @@ -45,23 +45,16 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf, size_t cou
>   	idxd_dev = confdev_to_idxd_dev(dev);
>   	if (is_idxd_dev(idxd_dev)) {
>   		alt_drv = driver_find("idxd", bus);
> -		if (!alt_drv)
> -			return -ENODEV;
>   	} else if (is_idxd_wq_dev(idxd_dev)) {
>   		struct idxd_wq *wq = confdev_to_wq(dev);
>   
> -		if (is_idxd_wq_kernel(wq)) {
> +		if (is_idxd_wq_kernel(wq))
>   			alt_drv = driver_find("dmaengine", bus);
> -			if (!alt_drv)
> -				return -ENODEV;
> -		} else if (is_idxd_wq_user(wq)) {
> +		else if (is_idxd_wq_user(wq))
>   			alt_drv = driver_find("user", bus);
> -			if (!alt_drv)
> -				return -ENODEV;
> -		} else {
> -			return -ENODEV;
> -		}
>   	}
> +	if (!alt_drv)
> +		return -ENODEV;
>   
>   	rc = device_driver_attach(alt_drv, dev);
>   	if (rc < 0)