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From: Kent Gibson <warthog618@gmail.com>
To: linux-kernel@vger.kernel.org,
	linux-gpio@vger.kernel.org,
	brgl@bgdev.pl,
	linus.walleij@linaro.org
Cc: Kent Gibson <warthog618@gmail.com>
Subject: [PATCH v2 1/3] gpiolib: cdev: Add INIT_KFIFO() for linereq events
Date: Wed, 29 May 2024 21:19:51 +0800
Message-Id: <20240529131953.195777-2-warthog618@gmail.com>
In-Reply-To: <20240529131953.195777-1-warthog618@gmail.com>
References: <20240529131953.195777-1-warthog618@gmail.com>
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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>
---
 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 9dad67ea2597..d4e47960cc98 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -1774,6 +1774,7 @@ 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;
--
2.39.2