On Tue, Oct 24, 2017 at 7:28 AM, Dmitry Torokhov
<dmitry.torokhov@xxxxxxxxx> wrote:
> parse_hid_report_descriptor() has a while (i < length) loop, which
> only guarantees that there's at least 1 byte in the buffer, but the
> loop body can read multiple bytes which causes out-of-bounds access.
>
> Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> ---
> drivers/input/tablet/gtco.c | 24 +++++++++++++++++-------
> 1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/input/tablet/gtco.c b/drivers/input/tablet/gtco.c
> index b796e891e2ee..0351203b8c24 100644
> --- a/drivers/input/tablet/gtco.c
> +++ b/drivers/input/tablet/gtco.c
> @@ -230,13 +230,24 @@ static void parse_hid_report_descriptor(struct gtco *device, char * report,
>
> /* Walk this report and pull out the info we need */
> while (i < length) {
> - prefix = report[i];
> -
> - /* Skip over prefix */
> - i++;
> + prefix = report[i++];
>
> /* Determine data size and save the data in the proper variable */
> - size = PREF_SIZE(prefix);
> + if (PREF_SIZE(prefix) < 1) {
AFAIU PREF_SIZE(prefix) == 0 is a perfectly valid item data size.
> + dev_err(ddev,
> + "Invalid size %d in element at offset %d\n",
> + PREF_SIZE(prefix), i);
> + break;
> + }
> +
> + size = 1U << (PREF_SIZE(prefix) - 1);
This formula doesn't work with PREF_SIZE(prefix) == 0.
> + if (i + size >= length) {
> + dev_err(ddev,
> + "Not enough data (need %d, have %d)\n",
> + i + size, length);
> + break;
> + }
> +
> switch (size) {
> case 1:
> data = report[i];
> @@ -244,8 +255,7 @@ static void parse_hid_report_descriptor(struct gtco *device, char * report,
> case 2:
> data16 = get_unaligned_le16(&report[i]);
> break;
> - case 3:
> - size = 4;
> + case 4:
> data32 = get_unaligned_le32(&report[i]);
> break;
> }
> --
> 2.15.0.rc0.271.g36b669edcc-goog
>
>
> --
> Dmitry
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