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

peter enderborg
2020-02-05T07:22:32Z

On 1/14/20 11:00 AM, Greg Kroah-Hartman wrote:
> From: Alan Stern <stern@rowland.harvard.edu>
>
> 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@syzkaller.appspotmail.com
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> CC: <stable@vger.kernel.org>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> 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.