From: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Subject: media: dvb_ca_en50221: prevent using slot_info for Spectre attacs
Git-commit: 4f5ab5d7a5e765ad231a132f82cec71de88b9aad
Patch-mainline: v4.18
References: bsc#1192802
Acked-by: Jiri Bohac <jbohac@suse.cz>

slot can be controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability,
as warned by smatch:
	drivers/media/dvb-core/dvb_ca_en50221.c:1479 dvb_ca_en50221_io_write() warn: potential spectre issue 'ca->slot_info' (local cap)

Acked-by: "Jasmin J." <jasmin@anw.at>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

diff --git a/drivers/media/dvb-core/dvb_ca_en50221.c b/drivers/media/dvb-core/dvb_ca_en50221.c
index 97365a863519..1310526b0d49 100644
--- a/drivers/media/dvb-core/dvb_ca_en50221.c
+++ b/drivers/media/dvb-core/dvb_ca_en50221.c
@@ -31,6 +31,7 @@
 #include <linux/slab.h>
 #include <linux/list.h>
 #include <linux/module.h>
+#include <linux/nospec.h>
 #include <linux/vmalloc.h>
 #include <linux/delay.h>
 #include <linux/spinlock.h>
@@ -1373,6 +1374,7 @@ static ssize_t dvb_ca_en50221_io_write(struct file *file,
 
 	if (slot >= ca->slot_count)
 		return -EINVAL;
+	slot = array_index_nospec(slot, ca->slot_count);
 
 	/* check if the slot is actually running */
 	if (ca->slot_info[slot].slot_state != DVB_CA_SLOTSTATE_RUNNING)
-- 
2.33.0