[net v3 1/3] net: core: set skb useful vars in __bpf_tx_skb

[xiangxia.m.yue@gmail.com]

From: Tonghao Zhang <xiangxia.m.yue@gmail.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.

bpf_redirect may be invoked in ingress or egress path, so
we set the *skb_iif unconditionally.

Fixes: a70b506efe89 ("bpf: enforce recursion limit on redirects")
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.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 8271624a19aa..225dc8743863 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, bpf_redirect may be invoked in ingress or egress path.
+	 * - 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