linux-kernel - Re: [PATCH] Input: avoid calling input_set_abs

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Date:   Tue, 2 May 2023 16:05:31 +1000
From:   Peter Hutterer <peter.hutterer@...-t.net>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     linux-input@...r.kernel.org,
        Teng Qi <starmiku1207184332@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: avoid calling input_set_abs_val() in the event
 handling core

On Mon, May 01, 2023 at 06:01:19PM -0700, Dmitry Torokhov wrote:
> input_abs_set_val() can nominally call input_alloc_absinfo() which may
> allocate memory with GFP_KERNEL flag. This does not happen when
> input_abs_set_val() is called by the input core to set current MT slot when
> handling a new input event, but it trips certain static analyzers.
> 
> Rearrange the code to access the relevant structures directly.
> 
> Reported-by: Teng Qi <starmiku1207184332@...il.com>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>

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

If git grep is to be believed, this is the only use of
input_abs_set_val. Maybe removing that function is an option?

Are there external drivers that rely on this (instead of sending an
event)?

Cheers,
  Peter

> ---
>  drivers/input/input.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/input.c b/drivers/input/input.c
> index 37e876d45eb9..f791d14ecf23 100644
> --- a/drivers/input/input.c
> +++ b/drivers/input/input.c
> @@ -190,6 +190,7 @@ static int input_handle_abs_event(struct input_dev *dev,
>  				  unsigned int code, int *pval)
>  {
>  	struct input_mt *mt = dev->mt;
> +	bool is_new_slot = false;
>  	bool is_mt_event;
>  	int *pold;
>  
> @@ -210,6 +211,7 @@ static int input_handle_abs_event(struct input_dev *dev,
>  		pold = &dev->absinfo[code].value;
>  	} else if (mt) {
>  		pold = &mt->slots[mt->slot].abs[code - ABS_MT_FIRST];
> +		is_new_slot = mt->slot != dev->absinfo[ABS_MT_SLOT].value;
>  	} else {
>  		/*
>  		 * Bypass filtering for multi-touch events when
> @@ -228,8 +230,8 @@ static int input_handle_abs_event(struct input_dev *dev,
>  	}
>  
>  	/* Flush pending "slot" event */
> -	if (is_mt_event && mt && mt->slot != input_abs_get_val(dev, ABS_MT_SLOT)) {
> -		input_abs_set_val(dev, ABS_MT_SLOT, mt->slot);
> +	if (is_new_slot) {
> +		dev->absinfo[ABS_MT_SLOT].value = mt->slot;
>  		return INPUT_PASS_TO_HANDLERS | INPUT_SLOT;
>  	}
>  
> -- 
> 2.40.1.495.gc816e09b53d-goog
> 
> 
> -- 
> Dmitry