[PATCH net-next 1/3] net/sched: act_mirred: account for TCA_MIRRED_BLOCKID in get_fill_size

[Victor Nogueira <victor@mojatatu.com>]

tcf_mirred_get_fill_size budgets only TCA_MIRRED_PARMS, but 
tcf_mirred_dump also emits TCA_MIRRED_BLOCKID whenever the action was 
created with a block instead of a device, so the budget falls 8 bytes
short of what the dump may produce for such actions.

Account for TCA_MIRRED_BLOCKID unconditionally: reading tcfm_blockid to
size it conditionally would race a concurrent replace, which can flip the 
action between device and block between sizing and dumping.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260824153903.4143642-1-victor@mojatatu.com
Co-developed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
---
 net/sched/act_mirred.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index 553342c55cf7..1c98e4d81ebe 100644
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -607,7 +607,8 @@ tcf_mirred_get_dev(const struct tc_action *a,
 
 static size_t tcf_mirred_get_fill_size(const struct tc_action *act)
 {
-	return nla_total_size(sizeof(struct tc_mirred));
+	return nla_total_size(sizeof(struct tc_mirred)) /* TCA_MIRRED_PARMS */
+		+ nla_total_size(sizeof(u32)); /* TCA_MIRRED_BLOCKID */
 }
 
 static void tcf_offload_mirred_get_dev(struct flow_action_entry *entry,
-- 
2.43.0