linux-kernel - Re: [PATCH] Input: Fix error handling in input_register

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Message-ID: <Z3t-uz2UaskMd_Wy@google.com>
Date: Sun, 5 Jan 2025 22:56:59 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Ma Ke <make24@...as.ac.cn>
Cc: jeff@...undy.com, bentiss@...nel.org, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] Input: Fix error handling in input_register_device()

Hi,

On Sun, Jan 05, 2025 at 05:24:48PM +0800, Ma Ke wrote:
> When device_add(&dev->dev) failed, calling put_device() to explicitly
> release dev->dev. Otherwise, it could cause double free problem.

How exactly allegedly missing put would cause double free?

> 
> As comment of device_add() says, if device_add() succeeds, you should
> call device_del() when you want to get rid of it. If device_add() has
> not succeeded, use only put_device() to drop the reference count.

As explained in the kerneldoc for input_register_device(), in case of
the failure caller must call input_free_device() which will do the
required "put" as well as will handle devm-allocated input devices
properly.

Adding call to put_device() as proposed by this patch will indeed
introduce double-free.

> 
> Found by code review.
> 
> Cc: stable@...r.kernel.org
> Fixes: 0cd587735205 ("Input: preallocate memory to hold event values")
> Signed-off-by: Ma Ke <make24@...as.ac.cn>
> ---
>  drivers/input/input.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/input/input.c b/drivers/input/input.c
> index 7f0477e04ad2..a0a36aa90ecc 100644
> --- a/drivers/input/input.c
> +++ b/drivers/input/input.c
> @@ -2456,8 +2456,10 @@ int input_register_device(struct input_dev *dev)
>  		input_dev_poller_finalize(dev->poller);
>  
>  	error = device_add(&dev->dev);
> -	if (error)
> +	if (error) {
> +		put_device(&dev->dev);
>  		goto err_devres_free;
> +	}
>  
>  	path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
>  	pr_info("%s as %s\n",
> -- 
> 2.25.1
> 

Thanks.

-- 
Dmitry