[PATCH 5.19 053/192] driver core: fix driver_set_override() issue with empty strings

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

commit 5666a274a6d54372d6b79b1f78682a9d827e679e upstream.

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.

Fixes: 23d99baf9d72 ("PCI: Use driver_set_override() instead of open-coding")
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: stable <stable@xxxxxxxxxx>
Reported-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
Tested-by: Huisong Li <lihuisong@xxxxxxxxxx>
Reviewed-by: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220901163734.3583106-1-gregkh@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/base/driver.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/base/driver.c
+++ b/drivers/base/driver.c
@@ -63,6 +63,12 @@ int driver_set_override(struct device *d
 	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);