net/sched: act_mirred: don't override retval if we already lost the skb

commit 166c2c8a6a4dc2e4ceba9e10cfe81c3e469e3210 upstream.

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>
[Minor conflict resolved due to code context change.]
Signed-off-by: Jianqi Ren <jianqi.ren.cn@windriver.com>
Signed-off-by: He Zhe <zhe.he@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index 91a19460cb5783eb767627aa661f01a013a20567..07b9f8335f05a443070c10a8d98c1298e76b5082 100644 (file)
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -256,31 +256,31 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 
        m_mac_header_xmit = READ_ONCE(m->tcfm_mac_header_xmit);
        m_eaction = READ_ONCE(m->tcfm_eaction);
+       is_redirect = tcf_mirred_is_act_redirect(m_eaction);
        retval = READ_ONCE(m->tcf_action);
        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)) || !netif_carrier_ok(dev)) {
                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;
         * since we can't easily detect the clsact caller, skip clone only for
         * ingress - that covers the TC S/W datapath.
         */
-       is_redirect = tcf_mirred_is_act_redirect(m_eaction);
        at_ingress = skb_at_tc_ingress(skb);
        use_reinsert = at_ingress && is_redirect &&
                       tcf_mirred_can_reinsert(retval);
        if (!use_reinsert) {
                skb2 = skb_clone(skb, GFP_ATOMIC);
                if (!skb2)
-                       goto out;
+                       goto err_cant_do;
        }
 
        want_ingress = tcf_mirred_act_wants_ingress(m_eaction);
@@ -323,12 +323,16 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
        }
 
        err = tcf_mirred_forward(want_ingress, skb2);
-       if (err) {
-out:
+       if (err)
                tcf_action_inc_overlimit_qstats(&m->common);
-               if (tcf_mirred_is_act_redirect(m_eaction))
-                       retval = TC_ACT_SHOT;
-       }
+       __this_cpu_dec(mirred_nest_level);
+
+       return retval;
+
+err_cant_do:
+       if (is_redirect)
+               retval = TC_ACT_SHOT;
+       tcf_action_inc_overlimit_qstats(&m->common);
        __this_cpu_dec(mirred_nest_level);
 
        return retval;