[PATCH net-next 09/11] netfilter: x_tables: Avoid a couple -Wflex-array-member-not-at-end warnings

[Florian Westphal <fw@strlen.de>]

From: "Gustavo A. R. Silva" <gustavoars@kernel.org>

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the TRAILING_OVERLAP() helper to fix the following warnings:

1 net/netfilter/x_tables.c:816:39: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
1 net/netfilter/x_tables.c:811:39: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM)
and a set of members that would otherwise follow it. This overlays
the trailing members onto the FAM while preserving the original
memory layout.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/x_tables.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index b39017c80548..9f837fb5ceb4 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -819,13 +819,17 @@ EXPORT_SYMBOL_GPL(xt_compat_match_to_user);
 
 /* non-compat version may have padding after verdict */
 struct compat_xt_standard_target {
-	struct compat_xt_entry_target t;
-	compat_uint_t verdict;
+	/* Must be last as it ends in a flexible-array member. */
+	TRAILING_OVERLAP(struct compat_xt_entry_target, t, data,
+		compat_uint_t verdict;
+	);
 };
 
 struct compat_xt_error_target {
-	struct compat_xt_entry_target t;
-	char errorname[XT_FUNCTION_MAXNAMELEN];
+	/* Must be last as it ends in a flexible-array member. */
+	TRAILING_OVERLAP(struct compat_xt_entry_target, t, data,
+		char errorname[XT_FUNCTION_MAXNAMELEN];
+	);
 };
 
 int xt_compat_check_entry_offsets(const void *base, const char *elems,
-- 
2.52.0