[PATCH] gpio: prevent potential speculation leaks in gpio_device_get_desc()

[Hagar Hemdan <hagarhem@xxxxxxxxxx>]

Users can call the gpio_ioctl() interface to get information about gpio
chip lines.
Lines on the chip are identified by an offset in the range
of [0,chip.lines).
Offset is copied from user and then used as an array index to get
the gpio descriptor without sanitization.

This change ensures that the offset is sanitized by
using "array_index_nospec" to mitigate any possibility of speculative
information leaks.

This bug was discovered and resolved using Coverity Static Analysis
Security Testing (SAST) by Synopsys, Inc.

Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")
Signed-off-by: Hagar Hemdan <hagarhem@xxxxxxxxxx>
---
Only compile tested, no access to HW.
---
 drivers/gpio/gpiolib-cdev.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 9dad67ea2597..215c03e6808f 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -20,6 +20,7 @@
 #include <linux/kfifo.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/nospec.h>
 #include <linux/overflow.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/poll.h>
@@ -2170,7 +2171,8 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
 	lflags = eventreq.handleflags;
 	eflags = eventreq.eventflags;
 
-	desc = gpio_device_get_desc(gdev, offset);
+	desc = gpio_device_get_desc(gdev,
+				array_index_nospec(offset, gdev->ngpio));
 	if (IS_ERR(desc))
 		return PTR_ERR(desc);
 
@@ -2477,7 +2479,8 @@ static int lineinfo_get_v1(struct gpio_chardev_data *cdev, void __user *ip,
 		return -EFAULT;
 
 	/* this doubles as a range check on line_offset */
-	desc = gpio_device_get_desc(cdev->gdev, lineinfo.line_offset);
+	desc = gpio_device_get_desc(cdev->gdev,
+				array_index_nospec(lineinfo.line_offset, cdev->gdev->ngpio));
 	if (IS_ERR(desc))
 		return PTR_ERR(desc);
 
@@ -2514,7 +2517,8 @@ static int lineinfo_get(struct gpio_chardev_data *cdev, void __user *ip,
 	if (memchr_inv(lineinfo.padding, 0, sizeof(lineinfo.padding)))
 		return -EINVAL;
 
-	desc = gpio_device_get_desc(cdev->gdev, lineinfo.offset);
+	desc = gpio_device_get_desc(cdev->gdev,
+				array_index_nospec(lineinfo.offset, cdev->gdev->ngpio));
 	if (IS_ERR(desc))
 		return PTR_ERR(desc);
 
-- 
2.40.1