Re: [PATCH 1/1] net: Fix use of proc_fs
From: Jakub Kicinski <kuba@kernel.org>
Date: 2020-12-12 19:49:48
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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 <redacted>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.
quoted hunk ↗ jump to hunk
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; }