Re: [net v6 1/2] net: core: set skb useful vars in __bpf_tx_skb

On Thu, Mar 24, 2022 at 11:16 PM Alexei Starovoitov
[off-list ref] wrote:

On Thu, Mar 24, 2022 at 6:57 AM [off-list ref] wrote:

quoted

From: Tonghao Zhang <redacted>

We may use bpf_redirect to redirect the packets to other
netdevice (e.g. ifb) in ingress or 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: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <redacted>
Cc: Song Liu <redacted>
Cc: Yonghong Song <redacted>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Antoine Tenart <atenart@kernel.org>
Cc: Alexander Lobakin <redacted>
Cc: Wei Wang <redacted>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tonghao Zhang <redacted>
---
 net/core/filter.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index a7044e98765e..c1f45d2e6b0a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -2107,7 +2107,15 @@ static inline int __bpf_tx_skb(struct net_device *dev, struct sk_buff *skb)
        }

        skb->dev = dev;
+       /* The target netdevice (e.g. ifb) may use the:
+        * - redirected
+        * - from_ingress
+        */
+#ifdef CONFIG_NET_CLS_ACT
+       skb_set_redirected(skb, skb->tc_at_ingress);
+#else
        skb_clear_tstamp(skb);
+#endif

I thought Daniel Nacked it a couple times already.
Please stop this spam.

Hi
Daniel rejected the 2/3 patch,
https://patchwork.kernel.org/project/netdevbpf/patch/20211208145459.9590-3-xiangxia.m.yue@gmail.com/
The reasons are as follows.
* 2/3 patch adds a check in fastpath.
* on egress, redirect skb to ifb is not useful.
but this patch fixes  redirect skb to ifb on ingress. I think it is
useful for us.

Hi
Daniel, can you review this patch ?

-- 
Best regards, Tonghao