netdev - [PATCH net v3] net: handle ARPHRD_PPP in dev_is_mac_header

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Message-Id: <20230823134102.1848881-1-nicolas.dichtel@6wind.com>
Date: Wed, 23 Aug 2023 15:41:02 +0200
From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
To: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Alexei Starovoitov <ast@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Guillaume Nault <gnault@...hat.com>
Cc: netdev@...r.kernel.org,
	bpf@...r.kernel.org,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	stable@...r.kernel.org,
	Siwar Zitouni <siwar.zitouni@...nd.com>
Subject: [PATCH net v3] net: handle ARPHRD_PPP in dev_is_mac_header_xmit()

The goal is to support a bpf_redirect() from an ethernet device (ingress)
to a ppp device (egress).
The l2 header is added automatically by the ppp driver, thus the ethernet
header should be removed.

CC: stable@...r.kernel.org
Fixes: 27b29f63058d ("bpf: add bpf_redirect() helper")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Tested-by: Siwar Zitouni <siwar.zitouni@...nd.com>
---

v2 -> v3:
 - add a comment in the code
 - rework the commit log

v1 -> v2:
 - I forgot the 'Tested-by' tag in the v1 :/

 include/linux/if_arp.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/if_arp.h b/include/linux/if_arp.h
index 1ed52441972f..10a1e81434cb 100644
--- a/include/linux/if_arp.h
+++ b/include/linux/if_arp.h
@@ -53,6 +53,10 @@ static inline bool dev_is_mac_header_xmit(const struct net_device *dev)
 	case ARPHRD_NONE:
 	case ARPHRD_RAWIP:
 	case ARPHRD_PIMREG:
+	/* PPP adds its l2 header automatically in ppp_start_xmit().
+	 * This makes it look like an l3 device to __bpf_redirect() and tcf_mirred_init().
+	 */
+	case ARPHRD_PPP:
 		return false;
 	default:
 		return true;
-- 
2.39.2