[PATCH] media: dvb_ca_en50221: prevent using slot_info for Spectre attacs

[Mauro Carvalho Chehab]

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)

Signed-off-by: Mauro Carvalho Chehab <mchehab+sams...@kernel.org>
---
 drivers/media/dvb-core/dvb_ca_en50221.c | 2 ++
 1 file changed, 2 insertions(+)

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>
@@ -1476,6 +1477,7 @@ 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);
        sl = &ca->slot_info[slot];
 
        /* check if the slot is actually running */
-- 
2.17.0