[PATCH AUTOSEL 6.6 42/83] gpiolib: cdev: Add INIT_KFIFO() for linereq events

Sasha Levin
2024-08-01T00:24:21Z

From: Kent Gibson <warthog618@gmail.com>

[ Upstream commit 35d848e7a1cbba2649ed98cf58e0cdc7ee560c7a ]

The initialisation of the linereq events kfifo relies on the struct being
zeroed and a subsequent call to kfifo_alloc(). The call to kfifo_alloc()
is deferred until edge detection is first enabled for the linereq. If the
kfifo is inadvertently accessed before the call to kfifo_alloc(), as was
the case in a recently discovered bug, it behaves as a FIFO of size 1 with
an element size of 0, so writes and reads to the kfifo appear successful
but copy no actual data.

As a defensive measure, initialise the kfifo with INIT_KFIFO() when the
events kfifo is constructed. This initialises the kfifo element size
and zeroes its data pointer, so any inadvertant access prior to the
kfifo_alloc() call will trigger an oops.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20240529131953.195777-2-warthog618@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpio/gpiolib-cdev.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index d526a4c91e82e..0b1531557f04f 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -1855,6 +1855,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)

mutex_init(&lr->config_mutex);
init_waitqueue_head(&lr->wait);
+ INIT_KFIFO(lr->events);
lr->event_buffer_size = ulr.event_buffer_size;
if (lr->event_buffer_size == 0)
lr->event_buffer_size = ulr.num_lines * 16;
--
2.43.0