Re: [PATCH 5.4 17/78] HID: Fix slab-out-of-bounds read in hid_field_extract (Broken!)

[peter enderborg]

On 1/14/20 11:00 AM, Greg Kroah-Hartman wrote:
> From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
>
> commit 8ec321e96e056de84022c032ffea253431a83c3c upstream.
>
> The syzbot fuzzer found a slab-out-of-bounds bug in the HID report
> handler.  The bug was caused by a report descriptor which included a
> field with size 12 bits and count 4899, for a total size of 7349
> bytes.
>
> The usbhid driver uses at most a single-page 4-KB buffer for reports.
> In the test there wasn't any problem about overflowing the buffer,
> since only one byte was received from the device.  Rather, the bug
> occurred when the HID core tried to extract the data from the report
> fields, which caused it to try reading data beyond the end of the
> allocated buffer.
>
> This patch fixes the problem by rejecting any report whose total
> length exceeds the HID_MAX_BUFFER_SIZE limit (minus one byte to allow
> for a possible report index).  In theory a device could have a report
> longer than that, but if there was such a thing we wouldn't handle it
> correctly anyway.
>
> Reported-and-tested-by: syzbot+09ef48aa58261464b621@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> CC: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>
> ---
>  drivers/hid/hid-core.c |    6 ++++++
>  1 file changed, 6 insertions(+)
>
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -288,6 +288,12 @@ static int hid_add_field(struct hid_pars
>  	offset = report->size;
>  	report->size += parser->global.report_size * parser->global.report_count;
>  
> +	/* Total size check: Allow for possible report index byte */
> +	if (report->size > (HID_MAX_BUFFER_SIZE - 1) << 3) {
> +		hid_err(parser->device, "report is too long\n");
> +		return -1;
> +	}
> +
>  	if (!parser->local.usage_index) /* Ignore padding fields */
>  		return 0;
>  
>
>
>
This patch breaks Elgato StreamDeck.