netfilter: bridge: stp fix reference to uninitialized data

The destination mac (destmac) is only valid if EBT_DESTMAC flag
is set. Fix by changing the order of the comparison to look for
the flag first.

Reported-by: [email protected]
Signed-off-by: Stephen Hemminger <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>

Author: shemminger

net/bridge/netfilter/ebt_stp.c

@@ -161,8 +161,8 @@ static int ebt_stp_mt_check(const struct xt_mtchk_param *par)
 	/* Make sure the match only receives stp frames */
 	if (!par->nft_compat &&
 	    (!ether_addr_equal(e->destmac, eth_stp_addr) ||
-	     !is_broadcast_ether_addr(e->destmsk) ||
-	     !(e->bitmask & EBT_DESTMAC)))
+	     !(e->bitmask & EBT_DESTMAC) ||
+	     !is_broadcast_ether_addr(e->destmsk)))
 		return -EINVAL;
 
 	return 0;