src: fix protocol context update on big-endian systems

There is an obscure bug on big-endian systems when trying to list a rule
containing the expression 'ct helper tftp' which triggers the assert()
call in mpz_get_type().

Florian identified the cause: ct_expr_pctx_update() is called for the
relational expression which calls mpz_get_uint32() to get RHS value
(assuming it is a protocol number). On big-endian systems, the
misinterpreted value exceeds UINT_MAX.

Expressions' pctx_update() callback should only be called for protocol
matches, so ct_meta_common_postprocess() lacked a check for 'left->flags
& EXPR_F_PROTOCOL' like the one already present in
payload_expr_pctx_update().

In order to fix this in a clean way, this patch introduces a wrapper
relational_expr_pctx_update() to be used instead of directly calling
LHS's pctx_update() callback which unifies the necessary checks (and
adds one more assert):

- assert(expr->ops->type == EXPR_RELATIONAL)
  -> This is new, just to ensure the wrapper is called properly.
- assert(expr->op == OP_EQ)
  -> This was moved from {ct,meta,payload}_expr_pctx_update().
- left->ops->pctx_update != NULL
  -> This was taken from expr_evaluate_relational(), a necessary
     requirement for the introduced wrapper to function at all.
- (left->flags & EXPR_F_PROTOCOL) != 0
  -> The crucial missing check which led to the problem.

Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/expression.c b/src/expression.c
index 273038e6..393c1b2b 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -600,6 +600,19 @@ struct expr *relational_expr_alloc(const struct location *loc, enum ops op,
 	return expr;
 }
 
+void relational_expr_pctx_update(struct proto_ctx *ctx,
+				 const struct expr *expr)
+{
+	const struct expr *left = expr->left;
+
+	assert(expr->ops->type == EXPR_RELATIONAL);
+	assert(expr->op == OP_EQ);
+
+	if (left->ops->pctx_update &&
+	    (left->flags & EXPR_F_PROTOCOL))
+		left->ops->pctx_update(ctx, expr);
+}
+
 static void range_expr_print(const struct expr *expr, struct output_ctx *octx)
 {
 	octx->numeric += NFT_NUMERIC_ALL + 1;