wil6210: Sanity check for reported DMA length

If Rx descriptor contains garbage, it is possible to access memory beyond
allocated buffer.

Check this condition and drop Rx if reported length is
unreasonable large
Signed-off-by: NVladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/wil6210/txrx.c

@@ -349,7 +349,13 @@ static struct sk_buff *wil_vring_reap_rx(struct wil6210_priv *wil,
 
 	d1 = wil_skb_rxdesc(skb);
 	*d1 = *d;
+	wil_vring_advance_head(vring, 1);
 	dmalen = le16_to_cpu(d1->dma.length);
+	if (dmalen > sz) {
+		wil_err(wil, "Rx size too large: %d bytes!\n", dmalen);
+		kfree(skb);
+		return NULL;
+	}
 	skb_trim(skb, dmalen);
 
 	wil->stats.last_mcs_rx = wil_rxdesc_mcs(d1);
@@ -362,8 +368,6 @@ static struct sk_buff *wil_vring_reap_rx(struct wil6210_priv *wil,
 	wil_hex_dump_txrx("Rx ", DUMP_PREFIX_NONE, 32, 4,
 			  (const void *)d, sizeof(*d), false);
 
-	wil_vring_advance_head(vring, 1);
-
 	/* no extra checks if in sniffer mode */
 	if (ndev->type != ARPHRD_ETHER)
 		return skb;