driver core: platform: Don't read past the end of "driver_override" buffer

BugLink: http://bugs.launchpad.net/bugs/1724783

commit bf563b01 upstream.

When printing the driver_override parameter when it is 4095 and 4094 bytes
long, the printing code would access invalid memory because we need count+1
bytes for printing.

Reject driver_override values of these lengths in driver_override_store().

This is in close analogy to commit 4efe874a ("PCI: Don't read past the
end of sysfs "driver_override" buffer") from Sasha Levin.

Fixes: 3d713e0e ("driver core: platform: add device binding path 'driver_override'")
Signed-off-by: Nicolai Stange <nstange@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/base/platform.c

@@ -834,7 +834,8 @@ static ssize_t driver_override_store(struct device *dev,
 	struct platform_device *pdev = to_platform_device(dev);
 	char *driver_override, *old, *cp;
 
-	if (count > PATH_MAX)
+	/* We need to keep extra room for a newline */
+	if (count >= (PAGE_SIZE - 1))
 		return -EINVAL;
 
 	driver_override = kstrndup(buf, count, GFP_KERNEL);