evaluate: support shifts larger than the width of the left operand

If we want to left-shift a value of narrower type and assign the result
to a variable of a wider type, we are constrained to only shifting up to
the width of the narrower type.  Thus:

  add rule t c meta mark set ip dscp << 2

works, but:

  add rule t c meta mark set ip dscp << 8

does not, even though the lvalue is large enough to accommodate the
result.

Upgrade the maximum length based on the statement datatype length, which
is provided via context, if it is larger than expression lvalue.

Update netlink_delinearize.c to handle the case where the length of a
shift expression does not match that of its left-hand operand.

Based on patch from Jeremy Sowden.

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

1 files changed, 44 insertions, 18 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 21d36049..b0a7fa76 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -1289,14 +1289,19 @@ static int constant_binop_simplify(struct eval_ctx *ctx, struct expr **expr)
 static int expr_evaluate_shift(struct eval_ctx *ctx, struct expr **expr)
 {
 	struct expr *op = *expr, *left = op->left, *right = op->right;
+	unsigned int shift = mpz_get_uint32(right->value);
+	unsigned int max_shift_len;
 
-	if (mpz_get_uint32(right->value) >= left->len)
+	if (ctx->stmt_len > left->len)
+		max_shift_len = ctx->stmt_len;
+	else
+		max_shift_len = left->len;
+
+	if (shift >= max_shift_len)
 		return expr_binary_error(ctx->msgs, right, left,
-					 "%s shift of %u bits is undefined "
-					 "for type of %u bits width",
+					 "%s shift of %u bits is undefined for type of %u bits width",
 					 op->op == OP_LSHIFT ? "Left" : "Right",
-					 mpz_get_uint32(right->value),
-					 left->len);
+					 shift, max_shift_len);
 
 	/* Both sides need to be in host byte order */
 	if (byteorder_conversion(ctx, &op->left, BYTEORDER_HOST_ENDIAN) < 0)
@@ -1306,7 +1311,7 @@ static int expr_evaluate_shift(struct eval_ctx *ctx, struct expr **expr)
 		return -1;
 
 	op->byteorder = BYTEORDER_HOST_ENDIAN;
-	op->len       = left->len;
+	op->len	      = max_shift_len;
 
 	if (expr_is_constant(left))
 		return constant_binop_simplify(ctx, expr);
@@ -1339,14 +1344,20 @@ static int expr_evaluate_binop(struct eval_ctx *ctx, struct expr **expr)
 {
 	struct expr *op = *expr, *left, *right;
 	const char *sym = expr_op_symbols[op->op];
+	unsigned int max_shift_len = ctx->ectx.len;
 
 	if (expr_evaluate(ctx, &op->left) < 0)
 		return -1;
 	left = op->left;
 
-	if (op->op == OP_LSHIFT || op->op == OP_RSHIFT)
+	if (op->op == OP_LSHIFT || op->op == OP_RSHIFT) {
+		if (left->len > max_shift_len)
+			max_shift_len = left->len;
+
 		__expr_set_context(&ctx->ectx, &integer_type,
-				   left->byteorder, ctx->ectx.len, 0);
+				   left->byteorder, max_shift_len, 0);
+	}
+
 	if (expr_evaluate(ctx, &op->right) < 0)
 		return -1;
 	right = op->right;
@@ -1865,6 +1876,7 @@ static int expr_evaluate_map(struct eval_ctx *ctx, struct expr **expr)
 	}
 
 	expr_set_context(&ctx->ectx, NULL, 0);
+	ctx->stmt_len = 0;
 	if (expr_evaluate(ctx, &map->map) < 0)
 		return -1;
 	if (expr_is_constant(map->map))
@@ -3000,20 +3012,34 @@ static int stmt_evaluate_meter(struct eval_ctx *ctx, struct stmt *stmt)
 
 static int stmt_evaluate_meta(struct eval_ctx *ctx, struct stmt *stmt)
 {
-	return stmt_evaluate_arg(ctx, stmt,
-				 stmt->meta.tmpl->dtype,
-				 stmt->meta.tmpl->len,
-				 stmt->meta.tmpl->byteorder,
-				 &stmt->meta.expr);
+	int ret;
+
+	ctx->stmt_len = stmt->meta.tmpl->len;
+
+	ret = stmt_evaluate_arg(ctx, stmt,
+				stmt->meta.tmpl->dtype,
+				stmt->meta.tmpl->len,
+				stmt->meta.tmpl->byteorder,
+				&stmt->meta.expr);
+	ctx->stmt_len = 0;
+
+	return ret;
 }
 
 static int stmt_evaluate_ct(struct eval_ctx *ctx, struct stmt *stmt)
 {
-	if (stmt_evaluate_arg(ctx, stmt,
-			      stmt->ct.tmpl->dtype,
-			      stmt->ct.tmpl->len,
-			      stmt->ct.tmpl->byteorder,
-			      &stmt->ct.expr) < 0)
+	int ret;
+
+	ctx->stmt_len = stmt->ct.tmpl->len;
+
+	ret = stmt_evaluate_arg(ctx, stmt,
+				stmt->ct.tmpl->dtype,
+				stmt->ct.tmpl->len,
+				stmt->ct.tmpl->byteorder,
+				&stmt->ct.expr);
+	ctx->stmt_len = 0;
+
+	if (ret < 0)
 		return -1;
 
 	if (stmt->ct.key == NFT_CT_SECMARK && expr_is_constant(stmt->ct.expr))