linux-kernel - [PATCH] gpiolib: cdev: fix NULL-pointer dereferences

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Date:   Fri, 25 Nov 2022 16:32:57 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Kent Gibson <warthog618@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH] gpiolib: cdev: fix NULL-pointer dereferences

From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

There are several places where we can crash the kernel by requesting
lines, unbinding the GPIO device, then calling any of the system calls
relevant to the GPIO character device's annonymous file descriptors:
ioctl(), read(), poll().

While I observed it with the GPIO simulator, it will also happen for any
of the GPIO devices that can be hot-unplugged - for instance any HID GPIO
expander (e.g. CP2112).

This affects both v1 and v2 uAPI.

Fix this by simply checking if the GPIO chip pointer is not NULL.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/gpio/gpiolib-cdev.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 0cb6b468f364..d5632742942a 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -201,6 +201,9 @@ static long linehandle_ioctl(struct file *file, unsigned int cmd,
 	unsigned int i;
 	int ret;
 
+	if (!lh->gdev->chip)
+		return -ENODEV;
+
 	switch (cmd) {
 	case GPIOHANDLE_GET_LINE_VALUES_IOCTL:
 		/* NOTE: It's okay to read values of output lines */
@@ -1384,6 +1387,9 @@ static long linereq_ioctl(struct file *file, unsigned int cmd,
 	struct linereq *lr = file->private_data;
 	void __user *ip = (void __user *)arg;
 
+	if (!lr->gdev->chip)
+		return -ENODEV;
+
 	switch (cmd) {
 	case GPIO_V2_LINE_GET_VALUES_IOCTL:
 		return linereq_get_values(lr, ip);
@@ -1716,6 +1722,9 @@ static __poll_t lineevent_poll(struct file *file,
 	struct lineevent_state *le = file->private_data;
 	__poll_t events = 0;
 
+	if (!le->gdev->chip)
+		return -ENODEV;
+
 	poll_wait(file, &le->wait, wait);
 
 	if (!kfifo_is_empty_spinlocked_noirqsave(&le->events, &le->wait.lock))
@@ -1740,6 +1749,9 @@ static ssize_t lineevent_read(struct file *file,
 	ssize_t ge_size;
 	int ret;
 
+	if (!le->gdev->chip)
+		return -ENODEV;
+
 	/*
 	 * When compatible system call is being used the struct gpioevent_data,
 	 * in case of at least ia32, has different size due to the alignment
@@ -1821,6 +1833,9 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd,
 	void __user *ip = (void __user *)arg;
 	struct gpiohandle_data ghd;
 
+	if (!le->gdev->chip)
+		return -ENODEV;
+
 	/*
 	 * We can get the value for an event line but not set it,
 	 * because it is input by definition.
-- 
2.37.2