From: Jakub Kicinski <kuba@kernel.org>
Date: Thu, 15 Feb 2024 06:33:46 -0800
Subject: net/sched: act_mirred: don't override retval if we already lost the skb
Patch-mainline: v6.8-rc6
Git-commit: 166c2c8a6a4dc2e4ceba9e10cfe81c3e469e3210
References: CVE-2024-26739 bsc#1222559

If we're redirecting the skb, and haven't called tcf_mirred_forward(),
yet, we need to tell the core to drop the skb by setting the retcode
to SHOT. If we have called tcf_mirred_forward(), however, the skb
is out of our hands and returning SHOT will lead to UaF.

Move the retval override to the error path which actually need it.

Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Fixes: e5cf1baf92cb ("act_mirred: use TC_ACT_REINSERT when possible")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 net/sched/act_mirred.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -213,13 +213,13 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 	dev = rcu_dereference_bh(m->tcfm_dev);
 	if (unlikely(!dev)) {
 		pr_notice_once("tc mirred: target device is gone\n");
-		goto out;
+		goto err_cant_do;
 	}
 
 	if (unlikely(!(dev->flags & IFF_UP))) {
 		net_notice_ratelimited("tc mirred to Houston: device %s is down\n",
 				       dev->name);
-		goto out;
+		goto err_cant_do;
 	}
 
 	/* we could easily avoid the clone only if called by ingress and clsact;
@@ -232,7 +232,7 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 	if (!use_reinsert) {
 		skb2 = skb_clone(skb, GFP_ATOMIC);
 		if (!skb2)
-			goto out;
+			goto err_cant_do;
 	}
 
 	/* If action's target direction differs than filter's direction,
@@ -273,14 +273,16 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 	else
 		err = netif_receive_skb(skb2);
 
-	if (err) {
-out:
+	if (err)
 		qstats_overlimit_inc(this_cpu_ptr(m->common.cpu_qstats));
-		if (tcf_mirred_is_act_redirect(m_eaction))
-			retval = TC_ACT_SHOT;
-	}
 
 	return retval;
+
+err_cant_do:
+	if (is_redirect)
+		retval = TC_ACT_SHOT;
+	qstats_overlimit_inc(this_cpu_ptr(m->common.cpu_qstats));
+	return retval;
 }
 
 static void tcf_stats_update(struct tc_action *a, u64 bytes, u32 packets,