evaluate: skip byteorder conversion for selector smaller than 2 bytes

Add unary expression to trigger byteorder conversion for host byteorder
selectors only if selectors length is larger or equal than 2 bytes.

 # cat test.nft
 table ip x {
        set test {
                type ipv4_addr . ether_addr . inet_proto
                flags interval
        }

        chain y {
                ip saddr . ether saddr . meta l4proto @test counter
        }
 }

 # nft -f test.nft
 ip x y
  [ meta load iiftype => reg 1 ]
  [ cmp eq reg 1 0x00000001 ]
  [ payload load 4b @ network header + 12 => reg 1 ]
  [ payload load 6b @ link header + 6 => reg 9 ]
  [ meta load l4proto => reg 11 ]
  [ byteorder reg 11 = hton(reg 11, 2, 1) ] <--- should not be here
  [ lookup reg 1 set test ]
  [ counter pkts 0 bytes 0 ]

Fixes: 1017d323cafa ("src: support for selectors with different byteorder with interval concatenations")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 1b430b72..92e009ef 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -199,12 +199,14 @@ static int byteorder_conversion(struct eval_ctx *ctx, struct expr **expr,
 
 			assert(basetype == TYPE_INTEGER);
 
-			op = byteorder_conversion_op(i, byteorder);
-			unary = unary_expr_alloc(&i->location, op, i);
-			if (expr_evaluate(ctx, &unary) < 0)
-				return -1;
+			if (div_round_up(i->len, BITS_PER_BYTE) >= 2) {
+				op = byteorder_conversion_op(i, byteorder);
+				unary = unary_expr_alloc(&i->location, op, i);
+				if (expr_evaluate(ctx, &unary) < 0)
+					return -1;
 
-			list_replace(&i->list, &unary->list);
+				list_replace(&i->list, &unary->list);
+			}
 		}
 
 		return 0;