[PATCH 4.9 13/31] HID: hid-lg4ff: Add check for empty lbuf

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

From: Anastasia Belova <abelova@astralinux.ru>

commit d180b6496143cd360c5d5f58ae4b9a8229c1f344 upstream.

If an empty buf is received, lbuf is also empty. So lbuf is
accessed by index -1.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: f31a2de3fe36 ("HID: hid-lg4ff: Allow switching of Logitech gaming wheels between compatibility modes")
Signed-off-by: Anastasia Belova <abelova@astralinux.ru>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/hid/hid-lg4ff.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/hid/hid-lg4ff.c
+++ b/drivers/hid/hid-lg4ff.c
@@ -880,6 +880,12 @@ static ssize_t lg4ff_alternate_modes_sto
 		return -ENOMEM;
 
 	i = strlen(lbuf);
+
+	if (i == 0) {
+		kfree(lbuf);
+		return -EINVAL;
+	}
+
 	if (lbuf[i-1] == '\n') {
 		if (i == 1) {
 			kfree(lbuf);