[PATCH 4.14 32/43] test_firmware: fix setting old custom fw path back on exit, second try

[Greg Kroah-Hartman]

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

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

From: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>

commit e538409257d0217a9bc715686100a5328db75a15 upstream.

Commit 65c79230576 tried to clear the custom firmware path on exit by
writing a single space to the firmware_class.path parameter.  This
doesn't work because nothing strips this space from the value stored
and fw_get_filesystem_firmware() only ignores zero-length paths.

Instead, write a null byte.

Fixes: 0a8adf58475 ("test: add firmware_class loader test")
Fixes: 65c79230576 ("test_firmware: fix setting old custom fw path back on exit")
Signed-off-by: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>
Acked-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>


---
 tools/testing/selftests/firmware/fw_filesystem.sh |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/firmware/fw_filesystem.sh
+++ b/tools/testing/selftests/firmware/fw_filesystem.sh
@@ -46,9 +46,11 @@ test_finish()
 		echo "$OLD_TIMEOUT" >/sys/class/firmware/timeout
 	fi
 	if [ "$OLD_FWPATH" = "" ]; then
-		OLD_FWPATH=" "
+		# A zero-length write won't work; write a null byte
+		printf '\000' >/sys/module/firmware_class/parameters/path
+	else
+		echo -n "$OLD_FWPATH" >/sys/module/firmware_class/parameters/path
 	fi
-	echo -n "$OLD_FWPATH" >/sys/module/firmware_class/parameters/path
 	rm -f "$FW"
 	rmdir "$FWPATH"
 }