On Tue, Oct 24, 2017 at 6:39 PM, Dmitry Torokhov
<dmitry.torokhov@xxxxxxxxx> wrote:
> On Tue, Oct 24, 2017 at 01:04:03PM +0200, Andrey Konovalov wrote:
>> 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.
>
> Fair enough. How about the below instead then?
>
> --
> Dmitry
>
>
> Input: gtco - fix potential out-of-bound access
>
> From: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
>
> 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 | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/input/tablet/gtco.c b/drivers/input/tablet/gtco.c
> index b796e891e2ee..7d8e9fb831c4 100644
> --- a/drivers/input/tablet/gtco.c
> +++ b/drivers/input/tablet/gtco.c
> @@ -230,13 +230,17 @@ 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);
> + size = (1U << PREF_SIZE(prefix)) >> 1;
> + if (size && i + size >= length) {
I think this should be >, not >=, as when i + size == length, item
data fits into the remaining space precisely. Also I don't see much
point in checking that size is not 0, but I don't mind it.
> + dev_err(ddev,
> + "Not enough data (need %d, have %d)\n",
> + i + size, length);
> + break;
> + }
> +
> switch (size) {
> case 1:
> data = report[i];
> @@ -244,8 +248,7 @@ 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;
> }
>
>
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