netkit: Assign missing bpf_net_context

During the introduction of struct bpf_net_context handling for
XDP-redirect, the netkit driver has been missed, which also requires it
because NETKIT_REDIRECT invokes skb_do_redirect() which is accessing the
per-CPU variables. Otherwise we see the following crash:

	BUG: kernel NULL pointer dereference, address: 0000000000000038
	bpf_redirect()
	netkit_xmit()
	dev_hard_start_xmit()

Set the bpf_net_context before invoking netkit_xmit() program within the
netkit driver.

Fixes: 401cb7dae813 ("net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.")
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20240912155620.1334587-1-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/netkit.c b/drivers/net/netkit.c
index 16789cd446e9e47fd738f12a9cde4e1eeef55fcf..3f4187102e773725f6d9cebad427385df28bdc3f 100644 (file)
--- a/drivers/net/netkit.c
+++ b/drivers/net/netkit.c
@@ -65,6 +65,7 @@ static struct netkit *netkit_priv(const struct net_device *dev)
 
 static netdev_tx_t netkit_xmit(struct sk_buff *skb, struct net_device *dev)
 {
+       struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
        struct netkit *nk = netkit_priv(dev);
        enum netkit_action ret = READ_ONCE(nk->policy);
        netdev_tx_t ret_dev = NET_XMIT_SUCCESS;
@@ -72,6 +73,7 @@ static netdev_tx_t netkit_xmit(struct sk_buff *skb, struct net_device *dev)
        struct net_device *peer;
        int len = skb->len;
 
+       bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
        rcu_read_lock();
        peer = rcu_dereference(nk->peer);
        if (unlikely(!peer || !(peer->flags & IFF_UP) ||
@@ -110,6 +112,7 @@ drop_stats:
                break;
        }
        rcu_read_unlock();
+       bpf_net_ctx_clear(bpf_net_ctx);
        return ret_dev;
 }