media: av7110: fix a spectre vulnerability

As warned by smatch:
	drivers/staging/media/av7110/av7110_ca.c:270 dvb_ca_ioctl() warn: potential spectre issue 'av7110->ci_slot' [w] (local cap)

There is a spectre-related vulnerability at the code. Fix it.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Author: mchehab

drivers/staging/media/av7110/av7110.h

@@ -88,6 +88,8 @@ struct infrared {
 	u32			ir_config;
 };
 
+#define MAX_CI_SLOTS	2
+
 /* place to store all the necessary device information */
 struct av7110 {
 	/* devices */
@@ -163,7 +165,7 @@ struct av7110 {
 
 	/* CA */
 
-	struct ca_slot_info	ci_slot[2];
+	struct ca_slot_info	ci_slot[MAX_CI_SLOTS];
 
 	enum av7110_video_mode	vidmode;
 	struct dmxdev		dmxdev;

drivers/staging/media/av7110/av7110_ca.c

@@ -26,23 +26,28 @@
 
 void CI_handle(struct av7110 *av7110, u8 *data, u16 len)
 {
+	unsigned slot_num;
+
 	dprintk(8, "av7110:%p\n", av7110);
 
 	if (len < 3)
 		return;
 	switch (data[0]) {
 	case CI_MSG_CI_INFO:
-		if (data[2] != 1 && data[2] != 2)
+		if (data[2] != 1 && data[2] != MAX_CI_SLOTS)
 			break;
+
+		slot_num = array_index_nospec(data[2] - 1, MAX_CI_SLOTS);
+
 		switch (data[1]) {
 		case 0:
-			av7110->ci_slot[data[2] - 1].flags = 0;
+			av7110->ci_slot[slot_num].flags = 0;
 			break;
 		case 1:
-			av7110->ci_slot[data[2] - 1].flags |= CA_CI_MODULE_PRESENT;
+			av7110->ci_slot[slot_num].flags |= CA_CI_MODULE_PRESENT;
 			break;
 		case 2:
-			av7110->ci_slot[data[2] - 1].flags |= CA_CI_MODULE_READY;
+			av7110->ci_slot[slot_num].flags |= CA_CI_MODULE_READY;
 			break;
 		}
 		break;
@@ -262,15 +267,19 @@ static int dvb_ca_ioctl(struct file *file, unsigned int cmd, void *parg)
 	case CA_GET_SLOT_INFO:
 	{
 		struct ca_slot_info *info = (struct ca_slot_info *)parg;
+		unsigned int slot_num;
 
 		if (info->num < 0 || info->num > 1) {
 			mutex_unlock(&av7110->ioctl_mutex);
 			return -EINVAL;
 		}
-		av7110->ci_slot[info->num].num = info->num;
-		av7110->ci_slot[info->num].type = FW_CI_LL_SUPPORT(av7110->arm_app) ?
-							CA_CI_LINK : CA_CI;
-		memcpy(info, &av7110->ci_slot[info->num], sizeof(struct ca_slot_info));
+		slot_num = array_index_nospec(info->num, MAX_CI_SLOTS);
+
+		av7110->ci_slot[slot_num].num = info->num;
+		av7110->ci_slot[slot_num].type = FW_CI_LL_SUPPORT(av7110->arm_app) ?
+						 CA_CI_LINK : CA_CI;
+		memcpy(info, &av7110->ci_slot[slot_num],
+		       sizeof(struct ca_slot_info));
 		break;
 	}