[nft PATCH v4 26/32] netlink_delinearize: add support for processing variable payload statement arguments

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If a user uses a variable payload expression in a payload statement, the
structure of the statement value is not handled by the existing
statement postprocessing function, so we need to extend it.

Signed-off-by: Jeremy Sowden <jeremy@xxxxxxxxxx>
---
 src/netlink_delinearize.c | 85 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 79 insertions(+), 6 deletions(-)

diff --git a/src/netlink_delinearize.c b/src/netlink_delinearize.c
index 4036646d57ac..e7042d6ae940 100644
--- a/src/netlink_delinearize.c
+++ b/src/netlink_delinearize.c
@@ -2862,7 +2862,7 @@ static void stmt_payload_binop_pp(struct rule_pp_ctx *ctx, struct expr *binop)
 	}
 }
 
-static bool stmt_payload_binop_postprocess_i(struct rule_pp_ctx *ctx)
+static bool stmt_payload_binop_postprocess_i_a(struct rule_pp_ctx *ctx)
 {
 	struct expr *expr, *binop, *payload, *value, *mask;
 	struct stmt *stmt = ctx->stmt;
@@ -2916,6 +2916,67 @@ static bool stmt_payload_binop_postprocess_i(struct rule_pp_ctx *ctx)
 	return true;
 }
 
+static bool stmt_payload_binop_postprocess_i_b(struct rule_pp_ctx *ctx)
+{
+	struct expr *expr, *payload, *mask, *xor;
+	struct stmt *stmt = ctx->stmt;
+	unsigned int shift;
+	mpz_t tmp, bitmask;
+
+	expr = stmt->payload.val;
+
+	if (expr->op != OP_XOR)
+		return false;
+
+	if (expr->left->etype != EXPR_BINOP)
+		return false;
+
+	if (expr->left->op != OP_AND)
+		return false;
+
+	if (expr->right->etype == EXPR_UNARY) {
+		/*
+		 * If the payload value was originally in a different byte-order
+		 * from the payload expression, there will be a byte-order
+		 * conversion to remove.
+		 */
+		xor = expr_get(expr->right->arg);
+		expr_free(expr->right);
+		expr->right = xor;
+	} else
+		xor = expr->right;
+
+	mask    = expr->left->right;
+	payload = expr->left->left;
+
+	mpz_init(tmp);
+	mpz_set(tmp, mask->value);
+
+	mpz_init_bitmask(bitmask, payload->len);
+	mpz_xor(bitmask, bitmask, mask->value);
+	mpz_set(mask->value, bitmask);
+	mpz_clear(bitmask);
+
+	if (payload_expr_trim(payload, mask, &ctx->pctx, &shift))
+		payload_match_postprocess(ctx, expr->left, payload);
+
+	if (!payload_is_known(payload)) {
+		mpz_set(mask->value, tmp);
+	} else {
+		if (shift) {
+			expr->right = expr_get(xor->left);
+			expr_free(xor);
+		}
+		expr_free(stmt->payload.expr);
+		stmt->payload.expr = expr_get(payload);
+		stmt->payload.val = expr_get(expr->right);
+		expr_free(expr);
+	}
+
+	mpz_clear(tmp);
+	return true;
+}
+
 static bool stmt_payload_binop_postprocess_ii(struct rule_pp_ctx *ctx)
 {
 	struct expr *expr, *payload, *value;
@@ -2983,21 +3044,30 @@ static bool stmt_payload_binop_postprocess_ii(struct rule_pp_ctx *ctx)
  * and a mask to clear the real payload offset/length.
  *
  * So check if we have one of the following binops:
- * I)
+ *
+ * Ia)
  *           binop (|)
  *       binop(&)   value/set
  * payload   value(mask)
  *
- * This is the normal case, the | RHS is the value the user wants
- * to set, the & RHS is the mask value that discards bits we need
+ * This is the normal constant case, the | RHS is the value the user
+ * wants to set, the & RHS is the mask value that discards bits we need
  * to clear but retains everything unrelated to the set operation.
  *
+ * Ib)
+ *         binop (^)
+ *       binop(&)   value/set
+ * payload   value(mask)
+ *
+ * The user wants to set a variable payload argument.  The ^ RHS is the
+ * variable expression.  The mask is as above.
+ *
  * IIa)
  *     binop (&)
  * payload   mask
  *
  * User specified a zero set value -- netlink bitwise decoding
- * discarded the redundant "| 0" part.  This is identical to I),
+ * discarded the redundant "| 0" part.  This is identical to Ia),
  * we can just set value to 0 after we inferred the real payload size.
  *
  * IIb)
@@ -3020,7 +3090,10 @@ static void stmt_payload_binop_postprocess(struct rule_pp_ctx *ctx)
 
 	switch (expr->left->etype) {
 	case EXPR_BINOP: /* I? */
-		if (stmt_payload_binop_postprocess_i(ctx))
+		if (stmt_payload_binop_postprocess_i_a(ctx))
+			return;
+
+		if (stmt_payload_binop_postprocess_i_b(ctx))
 			return;
 
 		break;
-- 
2.35.1




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