net/sched: act_mirred: Fix leak when redirecting to self on egress

Whenever a mirred redirect to self on egress happens, mirred allocates a
new skb (skb_to_send). The loop to self check was done after that
allocation, but was not freeing the newly allocated skb, causing a leak.

Fix this by moving the if-statement to before the allocation of the new
skb.

The issue was found by running the accompanying tdc test in 2/2
with config kmemleak enabled.
After a few minutes the kmemleak thread ran and reported the leak coming from
mirred.

Fixes: 1d856251a009 ("net/sched: act_mirred: fix loop detection")
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20260101135608.253079-2-jhs@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index 91c96cc625bd63eb07711a3e21333b21c3ee3b4d..05e0b14b57731498160c734ebf2d12f4f51472c3 100644 (file)
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -266,11 +266,22 @@ static int tcf_mirred_to_dev(struct sk_buff *skb, struct tcf_mirred *m,
                goto err_cant_do;
        }
 
+       want_ingress = tcf_mirred_act_wants_ingress(m_eaction);
+
+       at_ingress = skb_at_tc_ingress(skb);
+       if (dev == skb->dev && want_ingress == at_ingress) {
+               pr_notice_once("tc mirred: Loop (%s:%s --> %s:%s)\n",
+                              netdev_name(skb->dev),
+                              at_ingress ? "ingress" : "egress",
+                              netdev_name(dev),
+                              want_ingress ? "ingress" : "egress");
+               goto err_cant_do;
+       }
+
        /* we could easily avoid the clone only if called by ingress and clsact;
         * since we can't easily detect the clsact caller, skip clone only for
         * ingress - that covers the TC S/W datapath.
         */
-       at_ingress = skb_at_tc_ingress(skb);
        dont_clone = skb_at_tc_ingress(skb) && is_redirect &&
                tcf_mirred_can_reinsert(retval);
        if (!dont_clone) {
@@ -279,17 +290,6 @@ static int tcf_mirred_to_dev(struct sk_buff *skb, struct tcf_mirred *m,
                        goto err_cant_do;
        }
 
-       want_ingress = tcf_mirred_act_wants_ingress(m_eaction);
-
-       if (dev == skb->dev && want_ingress == at_ingress) {
-               pr_notice_once("tc mirred: Loop (%s:%s --> %s:%s)\n",
-                              netdev_name(skb->dev),
-                              at_ingress ? "ingress" : "egress",
-                              netdev_name(dev),
-                              want_ingress ? "ingress" : "egress");
-               goto err_cant_do;
-       }
-
        /* All mirred/redirected skbs should clear previous ct info */
        nf_reset_ct(skb_to_send);
        if (want_ingress && !at_ingress) /* drop dst for egress -> ingress */