evaluate: transfer right shifts to constant side

This provides a generic way to transfer shifts from the left hand side
to the right hand constant side of a relational expression when
performing transformations from the evaluation step.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/src/evaluate.c b/src/evaluate.c
index 7444d09ce17e9f4c89b6f3cf1ea7ab92569a814d..f862cd04342887ac8589d616fa91aef2a8414b66 100644 (file)
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -698,6 +698,7 @@ static int constant_binop_simplify(struct eval_ctx *ctx, struct expr **expr)
                break;
        case OP_LSHIFT:
                assert(left->byteorder == BYTEORDER_HOST_ENDIAN);
+               mpz_set(val, left->value);
                mpz_lshift_ui(val, mpz_get_uint32(right->value));
                mpz_and(val, val, mask);
                break;
@@ -1094,6 +1095,8 @@ static int binop_can_transfer(struct eval_ctx *ctx,
                        return expr_binary_error(ctx->msgs, right, left,
                                                 "Comparison is always false");
                return 1;
+       case OP_RSHIFT:
+               return 1;
        case OP_XOR:
                return 1;
        default:
@@ -1111,6 +1114,10 @@ static int binop_transfer_one(struct eval_ctx *ctx,
                (*right) = binop_expr_alloc(&(*right)->location, OP_RSHIFT,
                                            *right, expr_get(left->right));
                break;
+       case OP_RSHIFT:
+               (*right) = binop_expr_alloc(&(*right)->location, OP_LSHIFT,
+                                           *right, expr_get(left->right));
+               break;
        case OP_XOR:
                (*right) = binop_expr_alloc(&(*right)->location, OP_XOR,
                                            *right, expr_get(left->right));
@@ -1125,6 +1132,7 @@ static int binop_transfer_one(struct eval_ctx *ctx,
 static int binop_transfer(struct eval_ctx *ctx, struct expr **expr)
 {
        struct expr *left = (*expr)->left, *i, *next;
+       unsigned int shift;
        int err;
 
        if (left->ops->type != EXPR_BINOP)
@@ -1156,10 +1164,24 @@ static int binop_transfer(struct eval_ctx *ctx, struct expr **expr)
                return 0;
        }
 
-       left = expr_get((*expr)->left->left);
-       left->dtype = (*expr)->left->dtype;
-       expr_free((*expr)->left);
-       (*expr)->left = left;
+       switch (left->op) {
+       case OP_RSHIFT:
+               /* Mask out the bits the shift would have masked out */
+               shift = mpz_get_uint8(left->right->value);
+               mpz_bitmask(left->right->value, left->left->len);
+               mpz_lshift_ui(left->right->value, shift);
+               left->op = OP_AND;
+               break;
+       case OP_LSHIFT:
+       case OP_XOR:
+               left = expr_get((*expr)->left->left);
+               left->dtype = (*expr)->left->dtype;
+               expr_free((*expr)->left);
+               (*expr)->left = left;
+               break;
+       default:
+               BUG("invalid binop operation %u", left->op);
+       }
        return 0;
 }