linux-kernel - Re: [PATCH HID v2 02/11] HID: core: save one kmemdup during .probe()

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Message-ID: <20240912061029.GA559032@quokka>
Date: Thu, 12 Sep 2024 16:10:29 +1000
From: Peter Hutterer <peter.hutterer@...-t.net>
To: Benjamin Tissoires <bentiss@...nel.org>
Cc: Jiri Kosina <jikos@...nel.org>, Vicki Pfau <vi@...rift.com>,
	Shuah Khan <shuah@...nel.org>, linux-input@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org
Subject: Re: [PATCH HID v2 02/11] HID: core: save one kmemdup during .probe()

On Tue, Sep 10, 2024 at 11:43:38PM +0900, Benjamin Tissoires wrote:
> Turns out the first kmemdup is only required for the .report_fixup()
> driver callback. There is no need to do two kmemdup() in a raw in case

typo: "in a row"?

Cheers,
  Peter

> .report_fixup() is not present.
> 
> Signed-off-by: Benjamin Tissoires <bentiss@...nel.org>
> 
> ---
> 
> new in v2
> ---
>  drivers/hid/hid-core.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index a5f5415571cb..172746a082f9 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -1206,7 +1206,7 @@ int hid_open_report(struct hid_device *device)
>  	struct hid_item item;
>  	unsigned int size;
>  	const __u8 *start;
> -	__u8 *buf;
> +	__u8 *buf = NULL;
>  	const __u8 *end;
>  	const __u8 *next;
>  	int ret;
> @@ -1227,14 +1227,18 @@ int hid_open_report(struct hid_device *device)
>  	if (WARN_ON(!start))
>  		return -ENODEV;
>  
> -	buf = kmemdup(start, size, GFP_KERNEL);
> -	if (buf == NULL)
> -		return -ENOMEM;
> +	if (device->driver->report_fixup) {
> +		/*
> +		 * device->driver->report_fixup() needs to work
> +		 * on a copy of our report descriptor so it can
> +		 * change it.
> +		 */
> +		buf = kmemdup(start, size, GFP_KERNEL);
> +		if (buf == NULL)
> +			return -ENOMEM;
>  
> -	if (device->driver->report_fixup)
>  		start = device->driver->report_fixup(device, buf, &size);
> -	else
> -		start = buf;
> +	}
>  
>  	start = kmemdup(start, size, GFP_KERNEL);
>  	kfree(buf);
> 
> -- 
> 2.46.0
>