Input: synaptics-rmi4 - bound the F3A keymap to the GPIO count

commit 57c1091 upstream.

rmi_f3a_initialize() takes the GPIO count from the device query register
(f3a->gpio_count = buf & RMI_F3A_GPIO_COUNT, range 0..127).
rmi_f3a_map_gpios() then allocates gpio_key_map with
min(gpio_count, TRACKSTICK_RANGE_END) == at most 6 entries, but
rmi_f3a_attention() iterates the full gpio_count and dereferences
gpio_key_map[i], and input->keycodemax is set to the full gpio_count
while input->keycode points at the 6-entry allocation.

A device that reports gpio_count > 6 therefore causes an out-of-bounds
read of gpio_key_map[] on every attention interrupt, and out-of-bounds
accesses through the input core's default keymap ioctls: EVIOCGKEYCODE
reads past the buffer (leaking adjacent slab memory to user space) and
EVIOCSKEYCODE writes a caller-controlled value past it, for any process
able to open the evdev node, since input_default_getkeycode() and
input_default_setkeycode() only bound the index against keycodemax.

Size the keymap for the full gpio_count. The mapping loop is unchanged:
it still assigns only the first min(gpio_count, TRACKSTICK_RANGE_END)
entries; the remaining slots stay KEY_RESERVED (devm_kcalloc zero-fills)
and are skipped when reporting.

Fixes: 9e4c596 ("Input: synaptics-rmi4 - add support for F3A")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260614-b4-disp-818d6bda-v1-1-cf39a3615085@proton.me
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: bryamzxz

drivers/input/rmi4/rmi_f3a.c

@@ -132,7 +132,7 @@ static int rmi_f3a_map_gpios(struct rmi_function *fn, struct f3a_data *f3a,
 	int button_count = min_t(u8, f3a->gpio_count, TRACKSTICK_RANGE_END);
 
 	f3a->gpio_key_map = devm_kcalloc(&fn->dev,
-						button_count,
+						f3a->gpio_count,
 						sizeof(f3a->gpio_key_map[0]),
 						GFP_KERNEL);
 	if (!f3a->gpio_key_map) {