[PATCH] driver core: fix driver_set_override() issue with empty strings

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

Python likes to send an empty string for some sysfs files, including the
driver_override field.  When commit 23d99baf9d72 ("PCI: Use
driver_set_override() instead of open-coding") moved the PCI core to use
the driver core function instead of hand-rolling their own handler, this
showed up as a regression from some userspace tools, like DPDK.

Fix this up by actually looking at the length of the string first
instead of trusting that userspace got it correct.

Reported-by: Stephen Hemminger <stephen@networkplumber.org>
Fixes: 23d99baf9d72 ("PCI: Use driver_set_override() instead of open-coding")
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: stable <stable@kernel.org>
Tested-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/driver.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/base/driver.c b/drivers/base/driver.c
index 15a75afe6b84..676b6275d5b5 100644
--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -63,6 +63,12 @@ int driver_set_override(struct device *dev, const char **override,
 	if (len >= (PAGE_SIZE - 1))
 		return -EINVAL;
 
+	/*
+	 * Compute the real length of the string in case userspace sends us a
+	 * bunch of \0 characters like python likes to do.
+	 */
+	len = strlen(s);
+
 	if (!len) {
 		/* Empty string passed - clear override */
 		device_lock(dev);
-- 
2.37.3