From: Florian Westphal <fw@strlen.de>
Date: Wed, 22 Apr 2026 17:18:59 +0000 (+0200)
Subject: evaluate: remove zero shift expressions at eval stage
X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=HEAD;p=thirdparty%2Fnftables.git

evaluate: remove zero shift expressions at eval stage

There is a kernel patch (under review) that rejects 0-shifts from
control plane.  Remove zero-shifts at eval stage: they are
a no-op in any case.

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
---

diff --git a/src/evaluate.c b/src/evaluate.c
index 482708ae..8bb7b609 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -1454,6 +1454,12 @@ static int expr_evaluate_shift(struct eval_ctx *ctx, struct expr **expr)
 					 "shifts exceeding %u bits are not supported", UINT_MAX);
 
 	shift = mpz_get_uint32(right->value);
+	if (shift == 0) {
+		*expr = expr_get(left);
+		expr_free(op);
+		return 0;
+	}
+
 	if (ctx->stmt_len > left->len)
 		max_shift_len = ctx->stmt_len;
 	else