netlink_linearize: incorrect netlink bytecode with binary operation and flags

nft generates incorrect bytecode when combining flag datatype and binary
operations:

  # nft --debug=netlink add rule meh tcp_flags 'tcp flags & (fin | syn | rst | ack) syn'
ip
  [ meta load l4proto => reg 1 ]
  [ cmp eq reg 1 0x00000006 ]
  [ payload load 1b @ transport header + 13 => reg 1 ]
  [ bitwise reg 1 = ( reg 1 & 0x00000017 ) ^ 0x00000000 ]
  [ bitwise reg 1 = ( reg 1 & 0x00000002 ) ^ 0x00000000 ]
  [ cmp neq reg 1 0x00000000 ]

Note the double bitwise expression. The last two expressions are not
correct either since it should match on the syn flag, ie. 0x2.

After this patch, netlink bytecode generation looks correct:

 # nft --debug=netlink add rule meh tcp_flags 'tcp flags & (fin | syn | rst | ack) syn'
ip
  [ meta load l4proto => reg 1 ]
  [ cmp eq reg 1 0x00000006 ]
  [ payload load 1b @ transport header + 13 => reg 1 ]
  [ bitwise reg 1 = ( reg 1 & 0x00000017 ) ^ 0x00000000 ]
  [ cmp eq reg 1 0x00000002 ]

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

4 files changed, 93 insertions, 15 deletions

diff --git a/src/netlink_linearize.c b/src/netlink_linearize.c
index 9ab3ec3e..eb53ccec 100644
--- a/src/netlink_linearize.c
+++ b/src/netlink_linearize.c
@@ -481,23 +481,31 @@ static void netlink_gen_flagcmp(struct netlink_linearize_ctx *ctx,
 	netlink_gen_raw_data(zero, expr->right->byteorder, len, &nld);
 	netlink_gen_data(expr->right, &nld2);
 
-	nle = alloc_nft_expr("bitwise");
-	netlink_put_register(nle, NFTNL_EXPR_BITWISE_SREG, sreg);
-	netlink_put_register(nle, NFTNL_EXPR_BITWISE_DREG, sreg);
-	nftnl_expr_set_u32(nle, NFTNL_EXPR_BITWISE_LEN, len);
-	nftnl_expr_set(nle, NFTNL_EXPR_BITWISE_MASK, &nld2.value, nld2.len);
-	nftnl_expr_set(nle, NFTNL_EXPR_BITWISE_XOR, &nld.value, nld.len);
-	nft_rule_add_expr(ctx, nle, &expr->location);
-
-	nle = alloc_nft_expr("cmp");
-	netlink_put_register(nle, NFTNL_EXPR_CMP_SREG, sreg);
-	if (expr->op == OP_NEG)
+	if (expr->left->etype == EXPR_BINOP) {
+		nle = alloc_nft_expr("cmp");
+		netlink_put_register(nle, NFTNL_EXPR_CMP_SREG, sreg);
 		nftnl_expr_set_u32(nle, NFTNL_EXPR_CMP_OP, NFT_CMP_EQ);
-	else
-		nftnl_expr_set_u32(nle, NFTNL_EXPR_CMP_OP, NFT_CMP_NEQ);
+		nftnl_expr_set(nle, NFTNL_EXPR_CMP_DATA, nld2.value, nld2.len);
+		nft_rule_add_expr(ctx, nle, &expr->location);
+	} else {
+		nle = alloc_nft_expr("bitwise");
+		netlink_put_register(nle, NFTNL_EXPR_BITWISE_SREG, sreg);
+		netlink_put_register(nle, NFTNL_EXPR_BITWISE_DREG, sreg);
+		nftnl_expr_set_u32(nle, NFTNL_EXPR_BITWISE_LEN, len);
+		nftnl_expr_set(nle, NFTNL_EXPR_BITWISE_MASK, &nld2.value, nld2.len);
+		nftnl_expr_set(nle, NFTNL_EXPR_BITWISE_XOR, &nld.value, nld.len);
+		nft_rule_add_expr(ctx, nle, &expr->location);
 
-	nftnl_expr_set(nle, NFTNL_EXPR_CMP_DATA, nld.value, nld.len);
-	nft_rule_add_expr(ctx, nle, &expr->location);
+		nle = alloc_nft_expr("cmp");
+		netlink_put_register(nle, NFTNL_EXPR_CMP_SREG, sreg);
+		if (expr->op == OP_NEG)
+			nftnl_expr_set_u32(nle, NFTNL_EXPR_CMP_OP, NFT_CMP_EQ);
+		else
+			nftnl_expr_set_u32(nle, NFTNL_EXPR_CMP_OP, NFT_CMP_NEQ);
+
+		nftnl_expr_set(nle, NFTNL_EXPR_CMP_DATA, nld.value, nld.len);
+		nft_rule_add_expr(ctx, nle, &expr->location);
+	}
 
 	mpz_clear(zero);
 	release_register(ctx, expr->left);
diff --git a/tests/py/inet/tcp.t b/tests/py/inet/tcp.t
index 16e15b9f..983564ec 100644
--- a/tests/py/inet/tcp.t
+++ b/tests/py/inet/tcp.t
@@ -69,6 +69,8 @@ tcp flags != cwr;ok
 tcp flags == syn;ok
 tcp flags fin,syn / fin,syn;ok
 tcp flags != syn / fin,syn;ok
+tcp flags & (fin | syn | rst | ack) syn;ok;tcp flags syn / fin,syn,rst,ack
+tcp flags & (fin | syn | rst | ack) != syn;ok;tcp flags != syn / fin,syn,rst,ack
 tcp flags & (fin | syn | rst | psh | ack | urg | ecn | cwr) == fin | syn | rst | psh | ack | urg | ecn | cwr;ok;tcp flags == 0xff
 tcp flags { syn, syn | ack };ok
 tcp flags & (fin | syn | rst | psh | ack | urg) == { fin, ack, psh | ack, fin | psh | ack };ok
diff --git a/tests/py/inet/tcp.t.json b/tests/py/inet/tcp.t.json
index 590a3dee..033a4f22 100644
--- a/tests/py/inet/tcp.t.json
+++ b/tests/py/inet/tcp.t.json
@@ -1521,3 +1521,55 @@
     }
 ]
 
+# tcp flags & (fin | syn | rst | ack) syn
+[
+    {
+        "match": {
+            "left": {
+                "&": [
+                    {
+                        "payload": {
+                            "field": "flags",
+                            "protocol": "tcp"
+                        }
+                    },
+                    [
+                        "fin",
+                        "syn",
+                        "rst",
+                        "ack"
+                    ]
+                ]
+            },
+            "op": "==",
+            "right": "syn"
+        }
+    }
+]
+
+# tcp flags & (fin | syn | rst | ack) != syn
+[
+    {
+        "match": {
+            "left": {
+                "&": [
+                    {
+                        "payload": {
+                            "field": "flags",
+                            "protocol": "tcp"
+                        }
+                    },
+                    [
+                        "fin",
+                        "syn",
+                        "rst",
+                        "ack"
+                    ]
+                ]
+            },
+            "op": "!=",
+            "right": "syn"
+        }
+    }
+]
+
diff --git a/tests/py/inet/tcp.t.payload b/tests/py/inet/tcp.t.payload
index 7f302080..eaa7cd09 100644
--- a/tests/py/inet/tcp.t.payload
+++ b/tests/py/inet/tcp.t.payload
@@ -370,6 +370,22 @@ inet test-inet input
   [ bitwise reg 1 = ( reg 1 & 0x00000003 ) ^ 0x00000000 ]
   [ cmp neq reg 1 0x00000002 ]
 
+# tcp flags & (fin | syn | rst | ack) syn
+inet test-inet input
+  [ meta load l4proto => reg 1 ]
+  [ cmp eq reg 1 0x00000006 ]
+  [ payload load 1b @ transport header + 13 => reg 1 ]
+  [ bitwise reg 1 = ( reg 1 & 0x00000017 ) ^ 0x00000000 ]
+  [ cmp eq reg 1 0x00000002 ]
+
+# tcp flags & (fin | syn | rst | ack) != syn
+inet test-inet input
+  [ meta load l4proto => reg 1 ]
+  [ cmp eq reg 1 0x00000006 ]
+  [ payload load 1b @ transport header + 13 => reg 1 ]
+  [ bitwise reg 1 = ( reg 1 & 0x00000017 ) ^ 0x00000000 ]
+  [ cmp neq reg 1 0x00000002 ]
+
 # tcp flags & (fin | syn | rst | psh | ack | urg | ecn | cwr) == fin | syn | rst | psh | ack | urg | ecn | cwr
 inet test-inet input
   [ meta load l4proto => reg 1 ]