From: Jakub Kicinski <kuba@kernel.org>
To: Yonatan Linik <yonatanlinik@gmail.com>
Cc: davem@davemloft.net, ast@kernel.org, daniel@iogearbox.net,
kafai@fb.com, songliubraving@fb.com, yhs@fb.com, andriin@fb.com,
john.fastabend@gmail.com, kpsingh@chromium.org,
willemb@google.com, john.ogness@linutronix.de, arnd@arndb.de,
maowenan@huawei.com, colin.king@canonical.com,
orcohen@paloaltonetworks.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH 1/1] net: Fix use of proc_fs
Date: Sat, 12 Dec 2020 11:48:02 -0800 [thread overview]
Message-ID: <20201212114802.21a6b257@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <20201211163749.31956-2-yonatanlinik@gmail.com>
On Fri, 11 Dec 2020 18:37:49 +0200 Yonatan Linik wrote:
> 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@gmail.com>
Hm, I'm guessing you hit this on a kernel upgrade of a real system?
It seems like all callers to proc_create_net (and friends) interpret
NULL as an error, but only handful is protected by an ifdef.
I checked a few and none of them cares about the proc_dir_entry pointer
that gets returned. Should we perhaps rework the return values of the
function so that we can return success if !CONFIG_PROC_FS without
having to yield a pointer?
Obviously we can apply this fix so we can backport to 5.4 if you need
it. I think the ifdef is fine, since it's what other callers have.
> 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;
> }
next prev parent reply other threads:[~2020-12-12 19:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-11 16:37 [PATCH 0/1] net: Fix use of proc_fs Yonatan Linik
2020-12-11 16:37 ` [PATCH 1/1] " Yonatan Linik
2020-12-11 20:59 ` Arnd Bergmann
2020-12-12 8:39 ` Yonatan Linik
2020-12-12 19:48 ` Jakub Kicinski [this message]
2020-12-12 21:39 ` Yonatan Linik
2020-12-12 21:51 ` Jakub Kicinski
2020-12-13 9:48 ` Yonatan Linik
2020-12-14 19:07 ` Jakub Kicinski
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