linux-kernel - Re: [PATCH] Input: evdev - limit amount of data for writes

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Message-ID: <20240816001805.GA232957@quokka>
Date: Fri, 16 Aug 2024 10:18:05 +1000
From: Peter Hutterer <peter.hutterer@...-t.net>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: linux-input@...r.kernel.org, Jeff LaBundy <jeff@...undy.com>,
	Benjamin Tissoires <bentiss@...nel.org>,
	linux-kernel@...r.kernel.org, Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH] Input: evdev - limit amount of data for writes

On Thu, Aug 15, 2024 at 11:41:53AM -0700, Dmitry Torokhov wrote:
> Limit amount of data that can be written into an evdev instance at
> a given time to 4096 bytes (170 input events) to avoid holding
> evdev->mutex for too long and starving other users.
> 
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

I'd expect anything coming near 170 input events is going to trigger
SYN_DROPPED anyway, so:

Reviewed-by: Peter Hutterer <peter.hutterer@...-t.net>

thanks.

Cheers,
  Peter

> ---
>  drivers/input/evdev.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index a8ce3d140722..eb4906552ac8 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -498,6 +498,13 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer,
>  	struct input_event event;
>  	int retval = 0;
>  
> +	/*
> +	 * Limit amount of data we inject into the input subsystem so that
> +	 * we do not hold evdev->mutex for too long. 4096 bytes corresponds
> +	 * to 170 input events.
> +	 */
> +	count = min(count, 4096);
> +
>  	if (count != 0 && count < input_event_size())
>  		return -EINVAL;
>  
> -- 
> 2.46.0.184.g6999bdac58-goog
> 
> 
> -- 
> Dmitry