media: wl128x: prevent two potential buffer overflows

Smatch marks skb->data as untrusted so it warns that "evt_hdr->dlen"
can copy up to 255 bytes and we only have room for two bytes.  Even
if this comes from the firmware and we trust it, the new policy
generally is just to fix it as kernel hardenning.

I can't test this code so I tried to be very conservative.  I considered
not allowing "evt_hdr->dlen == 1" because it doesn't initialize the
whole variable but in the end I decided to allow it and manually
initialized "asic_id" and "asic_ver" to zero.

Fixes: e8454ff7 ("[media] drivers:media:radio: wl128x: FM Driver Common sources")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/radio/wl128x/fmdrv_common.c

@@ -489,7 +489,8 @@ int fmc_send_cmd(struct fmdev *fmdev, u8 fm_op, u16 type, void *payload,
 		return -EIO;
 	}
 	/* Send response data to caller */
-	if (response != NULL && response_len != NULL && evt_hdr->dlen) {
+	if (response != NULL && response_len != NULL && evt_hdr->dlen &&
+	    evt_hdr->dlen <= payload_len) {
 		/* Skip header info and copy only response data */
 		skb_pull(skb, sizeof(struct fm_event_msg_hdr));
 		memcpy(response, skb->data, evt_hdr->dlen);
@@ -583,6 +584,8 @@ static void fm_irq_handle_flag_getcmd_resp(struct fmdev *fmdev)
 		return;
 
 	fm_evt_hdr = (void *)skb->data;
+	if (fm_evt_hdr->dlen > sizeof(fmdev->irq_info.flag))
+		return;
 
 	/* Skip header info and copy only response data */
 	skb_pull(skb, sizeof(struct fm_event_msg_hdr));
@@ -1309,7 +1312,7 @@ static int load_default_rx_configuration(struct fmdev *fmdev)
 static int fm_power_up(struct fmdev *fmdev, u8 mode)
 {
 	u16 payload;
-	__be16 asic_id, asic_ver;
+	__be16 asic_id = 0, asic_ver = 0;
 	int resp_len, ret;
 	u8 fw_name[50];