netfilter: x_tables: guard option walkers against 1-byte tail reads

When the last byte of options is a non-single-byte option kind, walkers
that advance with i += op[i + 1] ? : 1 can read op[i + 1] past the end
of the option area.

Add an explicit i == optlen - 1 check before dereferencing op[i + 1]
in xt_tcpudp and xt_dccp option walkers.

Fixes: 2e4e6a1 ("[NETFILTER] x_tables: Abstraction layer for {ip,ip6,arp}_tables")
Signed-off-by: David Dull <monderasdor@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>

Author: AtomicElectronCreates

net/netfilter/xt_dccp.c

@@ -62,10 +62,10 @@ dccp_find_option(u_int8_t option,
 			return true;
 		}
 
-		if (op[i] < 2)
+		if (op[i] < 2 || i == optlen - 1)
 			i++;
 		else
-			i += op[i+1]?:1;
+			i += op[i + 1] ? : 1;
 	}
 
 	spin_unlock_bh(&dccp_buflock);

net/netfilter/xt_tcpudp.c

@@ -59,8 +59,10 @@ tcp_find_option(u_int8_t option,
 
 	for (i = 0; i < optlen; ) {
 		if (op[i] == option) return !invert;
-		if (op[i] < 2) i++;
-		else i += op[i+1]?:1;
+		if (op[i] < 2 || i == optlen - 1)
+			i++;
+		else
+			i += op[i + 1] ? : 1;
 	}
 
 	return invert;