netdev - Re: [Patch net] net: saving irq context for peernet2id()

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Date:   Thu, 20 Oct 2016 10:58:56 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Cc:     e@...draz.com, paul@...l-moore.com
Subject: Re: [Patch net] net: saving irq context for peernet2id()

On 10/20/2016 02:52 AM, Cong Wang wrote:
> A kernel warning inside __local_bh_enable_ip() was reported by people
> running SELinux, this is caused due to some SELinux functions
> (indirectly) call peernet2id() with IRQ disabled in process context,
> when we re-enable BH with IRQ disabled kernel complains. Shut up this
> warning by saving IRQ context in peernet2id(), BH is still implicitly
> disabled.

Not sure this suffices; kill_fasync() -> send_sigio() ->
send_sigio_to_task() -> sigio_perm() -> security_file_send_sigiotask()
-> selinux_file_send_sigiotask() -> ... -> audit_log() -> ... ->
peernet2id()

> 
> Fixes: bc51dddf98c9 ("netns: avoid disabling irq for netns id")
> Reported-by: Stephen Smalley <sds@...ho.nsa.gov>
> Reported-by: Elad Raz <e@...draz.com>
> Tested-by: Paul Moore <paul@...l-moore.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>  net/core/net_namespace.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index 989434f..17b52a2 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -230,11 +230,16 @@ int peernet2id_alloc(struct net *net, struct net *peer)
>  /* This function returns, if assigned, the id of a peer netns. */
>  int peernet2id(struct net *net, struct net *peer)
>  {
> +	unsigned long flags;
>  	int id;
>  
> -	spin_lock_bh(&net->nsid_lock);
> +	/* This is ugly, technically we only need to disable BH, however some
> +	 * callers (indirectly) call this with IRQ disabled, which implies
> +	 * that we should save the IRQ context here.
> +	 */
> +	spin_lock_irqsave(&net->nsid_lock, flags);
>  	id = __peernet2id(net, peer);
> -	spin_unlock_bh(&net->nsid_lock);
> +	spin_unlock_irqrestore(&net->nsid_lock, flags);
>  	return id;
>  }
>  EXPORT_SYMBOL(peernet2id);
>