netdev - Re: [PATCH net-next v2 1/2] inetpeer: add namespace support for inetpeer

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Date:	Tue, 05 Jun 2012 10:57:06 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Gao feng <gaofeng@...fujitsu.com>
Cc:	serge.hallyn@...onical.com, ebiederm@...ssion.com,
	herbert@...dor.apana.org.au, steffen.klassert@...unet.com,
	davem@...emloft.net, netdev@...r.kernel.org,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v2 1/2] inetpeer: add namespace support for
 inetpeer

On Tue, 2012-06-05 at 15:52 +0800, Gao feng wrote:

> +static void __net_exit inetpeer_net_exit(struct net *net)
> +{
> +	inetpeer_invalidate_tree(net, AF_INET);
> +	kfree(net->ipv4.peers);
> +
> +	inetpeer_invalidate_tree(net, AF_INET6);
> +	kfree(net->ipv6.peers);
> +}
> +

Are we 1000% sure no code ever run in inetpeer land after this call ?

I would add
	net->ipv4.peers = NULL;
	net->ipv6.peers = NULL;

to catch NULL deref instead of strange errors, just in case.

By the way, I think we have a bug in inetpeer_gc_worker()

Steffen ?

We have no rcu grace period to make sure the following is safe :

if (!atomic_read(&p->refcnt)) {
	list_del(&p->gc_list);
	kmem_cache_free(peer_cachep, p);
}

I'll post a fix like :

diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index d4d61b6..07731b5 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -137,7 +137,7 @@ static void inetpeer_gc_worker(struct work_struct *work)
 
 		n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
 
-		if (!atomic_read(&p->refcnt)) {
+		if (atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
 			list_del(&p->gc_list);
 			kmem_cache_free(peer_cachep, p);
 		}



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