[PATCH v2 07/33] HID: logitech-hidpp: fix off-by-one in G920 force-feedback slot tracking

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Logitech G920 firmware reports 64 total 1-based hardware effect slots,
reserving one slot for the built-in autocenter spring while allocating
the remaining 63 user effects across 1-based slots 2 through 64. Because
the driver subtracts the reserved slot count upfront before sizing and
bounds-checking its slot mapping table, the 63rd concurrent user effect
is assigned hardware slot 64 and exceeds the stored limit, so its slot
mapping is never recorded or released and remains leaked in wheel memory
across device close and reopen.

Keep the full hardware slot count for table sizing, lookups, and slot
bounds checks, and withhold the reserved slot count only when creating
the input force-feedback device.

Fixes: ff21a635dd1a ("HID: logitech-hidpp: Force feedback support for the Logitech G920")
Tested-by: Gideon Heinz <gideonheinz02@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/hid/hid-logitech-hidpp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index 53c171dfcf96..0264e4541edf 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -2872,7 +2872,7 @@ static int hidpp_ff_init(struct hidpp_device *hidpp,
 		for (j = 0; hidpp_ff_effects_v2[j] >= 0; j++)
 			set_bit(hidpp_ff_effects_v2[j], dev->ffbit);
 
-	error = input_ff_create(dev, num_slots);
+	error = input_ff_create(dev, num_slots - HIDPP_FF_RESERVED_SLOTS);
 
 	if (error) {
 		hid_err(dev, "Failed to create FF device!\n");
@@ -3486,7 +3486,7 @@ static int g920_get_config(struct hidpp_device *hidpp,
 		return -EPROTO;
 	}
 
-	data->num_effects = response.fap.params[0] - HIDPP_FF_RESERVED_SLOTS;
+	data->num_effects = response.fap.params[0];
 
 	/* reset all forces */
 	ret = hidpp_send_fap_command_sync(hidpp, data->feature_index,

-- 
2.56.0.542.g3ef89b7020-goog