linux-kernel - Re: [PATCH] HID: Fixed a crash in hid_report_raw

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Date:	Fri, 20 May 2011 12:02:04 -0400
From:	Valdis.Kletnieks@...edu
To:	Armando Visconti <armando.visconti@...com>
Cc:	jkosina@...e.cz, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: Fixed a crash in hid_report_raw_event() function.

On Thu, 19 May 2011 21:41:22 +0200, Armando Visconti said:
> I'm using a Data Modul EasyTouch USB multitouch controller,
> which is issuing a hid report with a size equals to 0. The rsize
> value gets set to 536870912 and Linux is crashing in the memset
> because the value is too big.
>
> Signed-off-by: Armando Visconti <armando.visconti@...com>
> ---
>  drivers/hid/hid-core.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index c3d6626..3e972e3 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -1045,6 +1045,9 @@ void hid_report_raw_event(struct hid_device *hid, int type, u8 *data, int size,
>
>  	rsize = ((report->size - 1) >> 3) + 1;
>
> +	if (rsize > HID_MAX_BUFFER_SIZE)
> +		rsize = HID_MAX_BUFFER_SIZE;
> +
>  	if (csize < rsize) {
>  		dbg_hid("report %d is too short, (%d < %d)\n", report->id,
>  				csize, rsize);

I'm thinking this is papering over the bug, and causing us to process a max-sized
buffer when the other end gave *zero* bytes back - this can't be good.

Probably should be more like this:

	if (!report->size) then	/* 
		rsize = MIN_VALID_SIZE; /* whatever it should be here */
	else {
		rsize = ((report->size - 1) >> 3) + 1;
		if (rsize > HID_MAX_BUFFER_SIZE)
			rsize = HID_MAX_BUFFER_SIZE;
	}

	if (csize < rsize) {


That last if() still looks squirrely - if we have an effectively zero rsize,
the report is short and the dbg_hid should fire.  Did we want "csize > rsize"
instead?



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