netdev - [PATCH bpf-next V4 5/5] bpf: make it possible to identify BPF redirected SKBs

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Message-ID: <160381603052.1435097.17996668799662432883.stgit@firesoul>
Date:   Tue, 27 Oct 2020 17:27:10 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     bpf@...r.kernel.org
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>, netdev@...r.kernel.org,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        maze@...gle.com, lmb@...udflare.com, shaun@...era.io,
        Lorenzo Bianconi <lorenzo@...nel.org>, marek@...udflare.com,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>, eyal.birger@...il.com
Subject: [PATCH bpf-next V4 5/5] bpf: make it possible to identify BPF
 redirected SKBs

This change makes it possible to identify SKBs that have been redirected
by TC-BPF (cls_act). This is needed for a number of cases.

(1) For collaborating with driver ifb net_devices.
(2) For avoiding starting generic-XDP prog on TC ingress redirect.

It is most important to fix XDP case(2), because this can break userspace
when a driver gets support for native-XDP. Imagine userspace loads XDP
prog on eth0, which fallback to generic-XDP, and it process TC-redirected
packets. When kernel is updated with native-XDP support for eth0, then the
program no-longer see the TC-redirected packets. Therefore it is important
to keep the order intact; that XDP runs before TC-BPF.

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 net/core/dev.c    |    2 ++
 net/sched/Kconfig |    1 +
 2 files changed, 3 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 445ccf92c149..930c165a607e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3870,6 +3870,7 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
 		return NULL;
 	case TC_ACT_REDIRECT:
 		/* No need to push/pop skb's mac_header here on egress! */
+		skb_set_redirected(skb, false);
 		skb_do_redirect(skb);
 		*ret = NET_XMIT_SUCCESS;
 		return NULL;
@@ -4959,6 +4960,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
 		 * redirecting to another netdev
 		 */
 		__skb_push(skb, skb->mac_len);
+		skb_set_redirected(skb, true);
 		if (skb_do_redirect(skb) == -EAGAIN) {
 			__skb_pull(skb, skb->mac_len);
 			*another = true;
diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index a3b37d88800e..a1bbaa8fd054 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -384,6 +384,7 @@ config NET_SCH_INGRESS
 	depends on NET_CLS_ACT
 	select NET_INGRESS
 	select NET_EGRESS
+	select NET_REDIRECT
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