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, 2 insertions, 4 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 758e7bbe..7fe738d8 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -746,7 +746,7 @@ static int ct_gen_nh_dependency(struct eval_ctx *ctx, struct expr *ct)
 				    constant_data_ptr(ct->ct.nfproto, left->len));
 	dep = relational_expr_alloc(&ct->location, OP_EQ, left, right);
 
-	left->ops->pctx_update(&ctx->pctx, dep);
+	relational_expr_pctx_update(&ctx->pctx, dep);
 
 	nstmt = expr_stmt_alloc(&dep->location, dep);
 
@@ -1635,9 +1635,7 @@ static int expr_evaluate_relational(struct eval_ctx *ctx, struct expr **expr)
 		 * Update protocol context for payload and meta iiftype
 		 * equality expressions.
 		 */
-		if (left->flags & EXPR_F_PROTOCOL &&
-		    left->ops->pctx_update)
-			left->ops->pctx_update(&ctx->pctx, rel);
+		relational_expr_pctx_update(&ctx->pctx, rel);
 
 		if (left->ops->type == EXPR_CONCAT)
 			return 0;