linux-kernel - [PATCH v8 02/20] gpiolib: cdev: replace strncpy with strscpy

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Date:   Wed,  9 Sep 2020 18:26:22 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        bgolaszewski@...libre.com, linus.walleij@...aro.org
Cc:     Kent Gibson <warthog618@...il.com>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH v8 02/20] gpiolib: cdev: replace strncpy with strscpy

Replace usage of strncpy with strscpy to remove -Wstringop-truncation
warnings.

The structs being populated are zeroed, to prevent stack leakage as
they are returned to userspace, so strscpy performs the equivalent
function without the warnings.

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Kent Gibson <warthog618@...il.com>
---

The memset in gpio_desc_to_lineinfo(), in conjunction with the strscpy,
is necessary as strncpy zero pads the remainder of the destination.
It also guarantees that the info cannot leak kernel stack to userspace.
This is useful here, but is even more important for the v2 info, that
this function is changed to generate in a subsequent patch, as that
struct contains padding and attribute arrays that also need to be
initialised.

 drivers/gpio/gpiolib-cdev.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index e95e3eab9867..8b012879fe3f 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -752,6 +752,7 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 	bool ok_for_pinctrl;
 	unsigned long flags;
 
+	memset(info, 0, sizeof(*info));
 	info->line_offset = gpio_chip_hwgpio(desc);
 	/*
 	 * This function takes a mutex so we must check this before taking
@@ -765,19 +766,11 @@ static void gpio_desc_to_lineinfo(struct gpio_desc *desc,
 
 	spin_lock_irqsave(&gpio_lock, flags);
 
-	if (desc->name) {
-		strncpy(info->name, desc->name, sizeof(info->name));
-		info->name[sizeof(info->name) - 1] = '\0';
-	} else {
-		info->name[0] = '\0';
-	}
+	if (desc->name)
+		strscpy(info->name, desc->name, sizeof(info->name));
 
-	if (desc->label) {
-		strncpy(info->consumer, desc->label, sizeof(info->consumer));
-		info->consumer[sizeof(info->consumer) - 1] = '\0';
-	} else {
-		info->consumer[0] = '\0';
-	}
+	if (desc->label)
+		strscpy(info->consumer, desc->label, sizeof(info->consumer));
 
 	/*
 	 * Userspace only need to know that the kernel is using this GPIO so
@@ -841,12 +834,10 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 		memset(&chipinfo, 0, sizeof(chipinfo));
 
-		strncpy(chipinfo.name, dev_name(&gdev->dev),
+		strscpy(chipinfo.name, dev_name(&gdev->dev),
 			sizeof(chipinfo.name));
-		chipinfo.name[sizeof(chipinfo.name)-1] = '\0';
-		strncpy(chipinfo.label, gdev->label,
+		strscpy(chipinfo.label, gdev->label,
 			sizeof(chipinfo.label));
-		chipinfo.label[sizeof(chipinfo.label)-1] = '\0';
 		chipinfo.lines = gdev->ngpio;
 		if (copy_to_user(ip, &chipinfo, sizeof(chipinfo)))
 			return -EFAULT;
-- 
2.28.0