netdev - [PATCH] net: core: set skb useful vars in __bpf_tx

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Message-Id: <20211029015431.32516-1-xiangxia.m.yue@gmail.com>
Date:   Fri, 29 Oct 2021 09:54:31 +0800
From:   xiangxia.m.yue@...il.com
To:     netdev@...r.kernel.org
Cc:     Tonghao Zhang <xiangxia.m.yue@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH] net: core: set skb useful vars in __bpf_tx_skb

From: Tonghao Zhang <xiangxia.m.yue@...il.com>

We may use bpf_redirect to redirect the packets to other
netdevice (e.g. ifb) in ingress and egress path.

The target netdevice may check the *skb_iif, *redirected
and *from_ingress, for example, if skb_iif or redirected
is 0, ifb will drop the packets.

Fixes: a70b506efe89 ("bpf: enforce recursion limit on redirects")
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
---
 net/core/filter.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 4bace37a6a44..2dbff0944768 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2107,9 +2107,19 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
 		return -ENETDOWN;
 	}
 
-	skb->dev = dev;
+	/* The target netdevice (e.g. ifb) may use the:
+	 * - skb_iif
+	 * - redirected
+	 * - from_ingress
+	 */
+	skb->skb_iif = skb->dev->ifindex;
+#ifdef CONFIG_NET_CLS_ACT
+	skb_set_redirected(skb, skb->tc_at_ingress);
+#else
 	skb->tstamp = 0;
+#endif
 
+	skb->dev = dev;
 	dev_xmit_recursion_inc();
 	ret = dev_queue_xmit(skb);
 	dev_xmit_recursion_dec();
-- 
2.27.0