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@gmail.com>
---
 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

Hi Dmitry,

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@gmail.com>

Reviewed-by: Jeff LaBundy <jeff@labundy.com>

> ---
>  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

Kind regards,
Jeff LaBundy

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@gmail.com>

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

Reviewed-by: Peter Hutterer <peter.hutterer@who-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

On Fri, Aug 16, 2024 at 10:18:05AM +1000, Peter Hutterer wrote:
> 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@gmail.com>
> 
> I'd expect anything coming near 170 input events is going to trigger
> SYN_DROPPED anyway, so:

This actually going the other direction (userspace -> kernel) so there
will be no SYN_DROPPED, at least on the way in.

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

Thanks for the review!

-- 
Dmitry