linux-kernel - [PATCH 1/1] net: Fix use of proc

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Date:   Fri, 11 Dec 2020 18:37:49 +0200
From:   Yonatan Linik <yonatanlinik@...il.com>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com, andriin@...com,
        john.fastabend@...il.com, kpsingh@...omium.org, willemb@...gle.com,
        john.ogness@...utronix.de, arnd@...db.de, maowenan@...wei.com,
        colin.king@...onical.com, orcohen@...oaltonetworks.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, Yonatan Linik <yonatanlinik@...il.com>
Subject: [PATCH 1/1] net: Fix use of proc_fs

proc_fs was used, in af_packet, without a surrounding #ifdef,
although there is no hard dependency on proc_fs.
That caused the initialization of the af_packet module to fail
when CONFIG_PROC_FS=n.

Specifically, proc_create_net() was used in af_packet.c,
and when it fails, packet_net_init() returns -ENOMEM.
It will always fail when the kernel is compiled without proc_fs,
because, proc_create_net() for example always returns NULL.

The calling order that starts in af_packet.c is as follows:
packet_init()
register_pernet_subsys()
register_pernet_operations()
__register_pernet_operations()
ops_init()
ops->init() (packet_net_ops.init=packet_net_init())
proc_create_net()

It worked in the past because register_pernet_subsys()'s return value
wasn't checked before this Commit 36096f2f4fa0 ("packet: Fix error path in
packet_init.").
It always returned an error, but was not checked before, so everything
was working even when CONFIG_PROC_FS=n.

The fix here is simply to add the necessary #ifdef.

Signed-off-by: Yonatan Linik <yonatanlinik@...il.com>
---
 net/packet/af_packet.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 2b33e977a905..031f2b593720 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4612,9 +4612,11 @@ static int __net_init packet_net_init(struct net *net)
 	mutex_init(&net->packet.sklist_lock);
 	INIT_HLIST_HEAD(&net->packet.sklist);

+#ifdef CONFIG_PROC_FS
 	if (!proc_create_net("packet", 0, net->proc_net, &packet_seq_ops,
 			sizeof(struct seq_net_private)))
 		return -ENOMEM;
+#endif /* CONFIG_PROC_FS */

 	return 0;
 }
-- 
2.25.1