linux-kernel - [PATCH 1/2] gpiolib: don't allow userspace to set values of input lines

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Message-Id: <20180716083424.11157-2-brgl@bgdev.pl>
Date:   Mon, 16 Jul 2018 10:34:23 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <brgl@...ev.pl>
Subject: [PATCH 1/2] gpiolib: don't allow userspace to set values of input lines

User space can currently both read and set values of input lines using
the character device. This was not allowed by the old sysfs interface
nor is it a correct behavior.

Check the first descriptor in the set for the OUT flag when asked to
set values and return -EPERM if the line is input.

Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
---
 drivers/gpio/gpiolib.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e11a3bb03820..57973524360d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -449,7 +449,13 @@ static long linehandle_ioctl(struct file *filep, unsigned int cmd,
 
 		return 0;
 	} else if (cmd == GPIOHANDLE_SET_LINE_VALUES_IOCTL) {
-		/* TODO: check if descriptors are really output */
+		/*
+		 * All line descriptors were created at once with the same
+		 * flags so just check if the first one is really output.
+		 */
+		if (!test_bit(FLAG_IS_OUT, &lh->descs[0]->flags))
+			return -EPERM;
+
 		if (copy_from_user(&ghd, ip, sizeof(ghd)))
 			return -EFAULT;
 
-- 
2.17.1