payload: don't adjust offsets of autogenerated dependency expressions

Pablo says:
  user reports that this is broken:
  nft --debug=netlink add rule bridge filter forward vlan id 100 vlan id set 200
[..]
    [ payload load 2b @ link header + 14 => reg 1 ]
[..]
    [ payload load 2b @ link header + 28 => reg 1 ]
    [ bitwise reg 1 = ( reg 1 & 0x000000f0 ) ^ 0x0000c800 ]
    [ payload write reg 1 => 2b @ link header + 14 csum_type 0 csum_off 0 csum_flags 0x0 ]

    offset says 28, it is assuming q-in-q, in this case it is mangling the
    existing header.

The problem here is that 'vlan id set 200' needs a read-modify-write
cycle because 'vlan id set' has to preserve bits located in the same byte area
as the vlan id.

The first 'payload load' at offset 14 is generated via 'vlan id 100',
this part is ok.

The second 'payload load' at offset 28 is the bogus one.
Its added as a dependency, but then adjusted because nft evaluation
considers this identical to 'vlan id 1 vlan id '2, where nft assumes
q-in-q.

To fix this, skip offset adjustments for raw expressions and mark the
dependency-generated payload instruction as such.

This is fine because raw payload operations assume that user specifies
base/offset/length manually.

Also add a test case for this.

Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>

6 files changed, 58 insertions, 1 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 8ebc7561..b39f4598 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -2554,6 +2554,7 @@ static int stmt_evaluate_payload(struct eval_ctx *ctx, struct stmt *stmt)
 			 payload_byte_offset * BITS_PER_BYTE,
 			 payload_byte_size * BITS_PER_BYTE);
 
+	payload_bytes->payload.is_raw = 1;
 	payload_bytes->payload.desc	 = payload->payload.desc;
 	payload_bytes->byteorder	 = payload->byteorder;
 
diff --git a/src/payload.c b/src/payload.c
index 97b60713..c662900b 100644
--- a/src/payload.c
+++ b/src/payload.c
@@ -115,7 +115,9 @@ static void payload_expr_pctx_update(struct proto_ctx *ctx,
 	assert(desc->base <= PROTO_BASE_MAX);
 	if (desc->base == base->base) {
 		assert(base->length > 0);
-		ctx->protocol[base->base].offset += base->length;
+
+		if (!left->payload.is_raw)
+			ctx->protocol[base->base].offset += base->length;
 	}
 	proto_ctx_update(ctx, desc->base, loc, desc);
 }
diff --git a/tests/py/bridge/vlan.t b/tests/py/bridge/vlan.t
index fd39d222..b506ee8d 100644
--- a/tests/py/bridge/vlan.t
+++ b/tests/py/bridge/vlan.t
@@ -43,3 +43,6 @@ ether type 8021ad vlan id 1 vlan type 8021q vlan id 2 vlan type ip ip protocol 6
 # illegal dependencies
 ether type ip vlan id 1;fail
 ether type ip vlan id 1 ip saddr 10.0.0.1;fail
+
+# mangling
+vlan id 1 vlan id set 2;ok
diff --git a/tests/py/bridge/vlan.t.json b/tests/py/bridge/vlan.t.json
index dae70170..e7640f9a 100644
--- a/tests/py/bridge/vlan.t.json
+++ b/tests/py/bridge/vlan.t.json
@@ -734,3 +734,30 @@
         }
     }
 ]
+
+# vlan id 1 vlan id set 2
+[
+    {
+        "match": {
+            "left": {
+                "payload": {
+                    "field": "id",
+                    "protocol": "vlan"
+                }
+            },
+            "op": "==",
+            "right": 1
+        }
+    },
+    {
+        "mangle": {
+            "key": {
+                "payload": {
+                    "field": "id",
+                    "protocol": "vlan"
+                }
+            },
+            "value": 2
+        }
+    }
+]
diff --git a/tests/py/bridge/vlan.t.payload b/tests/py/bridge/vlan.t.payload
index 49fd0ea7..6c8d595a 100644
--- a/tests/py/bridge/vlan.t.payload
+++ b/tests/py/bridge/vlan.t.payload
@@ -265,3 +265,14 @@ bridge
   [ cmp eq reg 1 0x00000008 ]
   [ payload load 1b @ network header + 9 => reg 1 ]
   [ cmp eq reg 1 0x00000006 ]
+
+# vlan id 1 vlan id set 2
+bridge
+  [ payload load 2b @ link header + 12 => reg 1 ]
+  [ cmp eq reg 1 0x00000081 ]
+  [ payload load 2b @ link header + 14 => reg 1 ]
+  [ bitwise reg 1 = ( reg 1 & 0x0000ff0f ) ^ 0x00000000 ]
+  [ cmp eq reg 1 0x00000100 ]
+  [ payload load 2b @ link header + 14 => reg 1 ]
+  [ bitwise reg 1 = ( reg 1 & 0x000000f0 ) ^ 0x00000200 ]
+  [ payload write reg 1 => 2b @ link header + 14 csum_type 0 csum_off 0 csum_flags 0x0 ]
diff --git a/tests/py/bridge/vlan.t.payload.netdev b/tests/py/bridge/vlan.t.payload.netdev
index 1a2c08ae..d2c7d74a 100644
--- a/tests/py/bridge/vlan.t.payload.netdev
+++ b/tests/py/bridge/vlan.t.payload.netdev
@@ -309,3 +309,16 @@ netdev
   [ cmp eq reg 1 0x00000008 ]
   [ payload load 1b @ network header + 9 => reg 1 ]
   [ cmp eq reg 1 0x00000006 ]
+
+# vlan id 1 vlan id set 2
+netdev
+  [ meta load iiftype => reg 1 ]
+  [ cmp eq reg 1 0x00000001 ]
+  [ payload load 2b @ link header + 12 => reg 1 ]
+  [ cmp eq reg 1 0x00000081 ]
+  [ payload load 2b @ link header + 14 => reg 1 ]
+  [ bitwise reg 1 = ( reg 1 & 0x0000ff0f ) ^ 0x00000000 ]
+  [ cmp eq reg 1 0x00000100 ]
+  [ payload load 2b @ link header + 14 => reg 1 ]
+  [ bitwise reg 1 = ( reg 1 & 0x000000f0 ) ^ 0x00000200 ]
+  [ payload write reg 1 => 2b @ link header + 14 csum_type 0 csum_off 0 csum_flags 0x0 ]