[PATCH libevdev 6/6] Drop invalid ABS_MT_TRACKING_ID changes
Benjamin Tissoires
benjamin.tissoires at gmail.com
Wed Apr 2 16:33:37 PDT 2014
On Tue, Apr 1, 2014 at 10:17 PM, Peter Hutterer
<peter.hutterer at who-t.net> wrote:
> Follow-up to
> commit 41334b5b40cd5456f5f584b55d8888aaafa1f26e
> Author: Peter Hutterer <peter.hutterer at who-t.net>
> Date: Thu Mar 6 11:54:00 2014 +1000
>
> If the tracking ID changes during SYN_DROPPED, terminate the touch first
>
> In normal mode, we may get double tracking ID events in the same slot, but
> only if we either have a user-generated event sequence (uinput) or a malicious
> device that tries to send data on a slot > dev->num_slots.
> Since the client is unlikely to be able to handle these events, discard the
> ABS_MT_TRACKING_ID completely. This is a bug somewhere in the stack, so
> complain and hobble on along.
>
> Note: the kernel doesn't allow that, but we cap to num_slots anyway, see
> 66fee1bec4c4b021e1b54adcd775cf6e2aa84869.
>
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> ---
> libevdev/libevdev.c | 31 +++++++++++++-----
> test/test-libevdev-events.c | 76 +++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 100 insertions(+), 7 deletions(-)
>
> diff --git a/libevdev/libevdev.c b/libevdev/libevdev.c
> index 2262284..b035607 100644
> --- a/libevdev/libevdev.c
> +++ b/libevdev/libevdev.c
> @@ -883,10 +883,12 @@ read_more_events(struct libevdev *dev)
>
> /**
> * Sanitize/modify events where needed.
> - * @return 0 if untouched, 1 if modified.
> + * @return 0 if untouched, 1 if modified, -1 if to be discarded
Seems OK, but I really hope you will not add more return codes to
sanitize events. It's going to be very complicate to understand it
from a caller point of view.
> */
> static inline int
> -sanitize_event(const struct libevdev *dev, struct input_event *ev)
> +sanitize_event(const struct libevdev *dev,
> + struct input_event *ev,
> + enum SyncState sync_state)
> {
> if (unlikely(dev->num_slots > -1 &&
> libevdev_event_is_code(ev, EV_ABS, ABS_MT_SLOT) &&
> @@ -896,6 +898,21 @@ sanitize_event(const struct libevdev *dev, struct input_event *ev)
> dev->name, ev->value, dev->num_slots - 1);
> ev->value = dev->num_slots - 1;
> return 1;
> +
> + /* Drop any invalid tracking IDs, they are only supposed to go from
> + N to -1 or from -1 to N. Never from -1 to -1, or N to M. Very
> + unlikely to ever happen from a real device.
> + */
> + } else if (unlikely(sync_state == SYNC_NONE &&
> + dev->num_slots > -1 &&
> + libevdev_event_is_code(ev, EV_ABS, ABS_MT_TRACKING_ID) &&
> + ((ev->value == -1 &&
> + *slot_value(dev, dev->current_slot, ABS_MT_TRACKING_ID) == -1) ||
> + (ev->value != -1 &&
> + *slot_value(dev, dev->current_slot, ABS_MT_TRACKING_ID) != -1)))) {
> + log_bug("Device \"%s\" received a double tracking ID %d in slot %d.\n",
> + dev->name, ev->value, dev->current_slot);
> + return -1;
> }
>
> return 0;
> @@ -937,8 +954,8 @@ libevdev_next_event(struct libevdev *dev, unsigned int flags, struct input_event
> of the device too */
> while (queue_shift(dev, &e) == 0) {
> dev->queue_nsync--;
> - sanitize_event(dev, &e);
> - update_state(dev, &e);
> + if (sanitize_event(dev, &e, dev->sync_state) != -1)
> + update_state(dev, &e);
> }
>
> dev->sync_state = SYNC_NONE;
> @@ -968,8 +985,8 @@ libevdev_next_event(struct libevdev *dev, unsigned int flags, struct input_event
> if (queue_shift(dev, ev) != 0)
> return -EAGAIN;
>
> - sanitize_event(dev, ev);
> - update_state(dev, ev);
> + if (sanitize_event(dev, ev, dev->sync_state) != -1)
> + update_state(dev, ev);
>
> /* if we disabled a code, get the next event instead */
> } while(!libevdev_has_event_code(dev, ev->type, ev->code));
> @@ -1166,7 +1183,7 @@ libevdev_set_event_value(struct libevdev *dev, unsigned int type, unsigned int c
> e.code = code;
> e.value = value;
>
> - if (sanitize_event(dev, &e))
> + if (sanitize_event(dev, &e, SYNC_NONE))
> return -1;
>
> switch(type) {
> diff --git a/test/test-libevdev-events.c b/test/test-libevdev-events.c
> index fda7617..921eda6 100644
> --- a/test/test-libevdev-events.c
> +++ b/test/test-libevdev-events.c
> @@ -1424,6 +1424,81 @@ START_TEST(test_mt_slot_ranges_invalid)
> }
> END_TEST
>
> +START_TEST(test_mt_tracking_id_discard)
> +{
> + struct uinput_device* uidev;
> + struct libevdev *dev;
> + int rc;
> + struct input_event ev;
> + struct input_absinfo abs[6];
> +
> + memset(abs, 0, sizeof(abs));
> + abs[0].value = ABS_X;
> + abs[0].maximum = 1000;
> + abs[1].value = ABS_MT_POSITION_X;
> + abs[1].maximum = 1000;
> +
> + abs[2].value = ABS_Y;
> + abs[2].maximum = 1000;
> + abs[3].value = ABS_MT_POSITION_Y;
> + abs[3].maximum = 1000;
> +
> + abs[4].value = ABS_MT_SLOT;
> + abs[4].maximum = 10;
> + abs[5].value = ABS_MT_TRACKING_ID;
> + abs[5].maximum = 500;
> +
> + rc = test_create_abs_device(&uidev, &dev,
> + 6, abs,
> + EV_SYN, SYN_REPORT,
> + -1);
> +
> + uinput_device_event(uidev, EV_ABS, ABS_MT_SLOT, 1);
> + uinput_device_event(uidev, EV_ABS, ABS_MT_TRACKING_ID, 1);
> + uinput_device_event(uidev, EV_SYN, SYN_REPORT, 0);
> +
> + /* second tracking ID on same slot */
> + uinput_device_event(uidev, EV_ABS, ABS_MT_TRACKING_ID, 2);
> + uinput_device_event(uidev, EV_SYN, SYN_REPORT, 0);
> +
> + libevdev_set_log_function(test_logfunc_ignore_error, NULL);
> +
> + rc = libevdev_next_event(dev, LIBEVDEV_READ_FLAG_NORMAL, &ev);
> + ck_assert_int_eq(rc, LIBEVDEV_READ_STATUS_SUCCESS);
> + ck_assert_int_eq(ev.type, EV_ABS);
> + ck_assert_int_eq(ev.code, ABS_MT_SLOT);
> + ck_assert_int_eq(ev.value, 1);
> +
> + rc = libevdev_next_event(dev, LIBEVDEV_READ_FLAG_NORMAL, &ev);
> + ck_assert_int_eq(rc, LIBEVDEV_READ_STATUS_SUCCESS);
> + ck_assert_int_eq(ev.type, EV_ABS);
> + ck_assert_int_eq(ev.code, ABS_MT_TRACKING_ID);
> + ck_assert_int_eq(ev.value, 1);
> +
> + rc = libevdev_next_event(dev, LIBEVDEV_READ_FLAG_NORMAL, &ev);
> + ck_assert_int_eq(rc, LIBEVDEV_READ_STATUS_SUCCESS);
> + ck_assert_int_eq(ev.type, EV_SYN);
> + ck_assert_int_eq(ev.code, SYN_REPORT);
> + ck_assert_int_eq(ev.value, 0);
> +
> + rc = libevdev_next_event(dev, LIBEVDEV_READ_FLAG_NORMAL, &ev);
> + ck_assert_int_eq(rc, LIBEVDEV_READ_STATUS_SUCCESS);
> +
> + /* expect tracking ID discarded */
> +
> + rc = libevdev_next_event(dev, LIBEVDEV_READ_FLAG_NORMAL, &ev);
> + ck_assert_int_eq(rc, LIBEVDEV_READ_STATUS_SUCCESS);
> + ck_assert_int_eq(ev.type, EV_SYN);
> + ck_assert_int_eq(ev.code, SYN_REPORT);
> + ck_assert_int_eq(ev.value, 0);
shouldn't we also test for two consecutive ABS_MT_TRACKING_ID == -1?
The code checks for it, and it will also be a problem if a device
closes twice a slot.
Cheers,
Benjamin
> +
> + libevdev_set_log_function(test_logfunc_abort_on_error, NULL);
> +
> + uinput_device_free(uidev);
> + libevdev_free(dev);
> +}
> +END_TEST
> +
> START_TEST(test_ev_rep_values)
> {
> struct uinput_device* uidev;
> @@ -1719,6 +1794,7 @@ libevdev_events(void)
> tcase_add_test(tc, test_mt_event_values);
> tcase_add_test(tc, test_mt_event_values_invalid);
> tcase_add_test(tc, test_mt_slot_ranges_invalid);
> + tcase_add_test(tc, test_mt_tracking_id_discard);
> tcase_add_test(tc, test_ev_rep_values);
> suite_add_tcase(s, tc);
>
> --
> 1.9.0
>
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