[PATCH 4.8 009/138] gpio: GPIO_GET_CHIPINFO_IOCTL: Fix line offset validation

[Greg Kroah-Hartman]

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lars-Peter Clausen <lars@xxxxxxxxxx>

commit 1f1cc4566bd9dd8d3cf19965a4b6392143618536 upstream.

The current line offset validation is off by one. Depending on the data
stored behind the descs array this can either cause undefined behavior or
disclose arbitrary, potentially sensitive, memory to the issuing userspace
application.

Make sure that offset is within the bounds of the desc array.

Fixes: 521a2ad6f862 ("gpio: add userspace ABI for GPIO line information")
Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpio/gpiolib.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -837,7 +837,7 @@ static long gpio_ioctl(struct file *filp
 
 		if (copy_from_user(&lineinfo, ip, sizeof(lineinfo)))
 			return -EFAULT;
-		if (lineinfo.line_offset > gdev->ngpio)
+		if (lineinfo.line_offset >= gdev->ngpio)
 			return -EINVAL;
 
 		desc = &gdev->descs[lineinfo.line_offset];