netdev - RE: [PATCH nf-next] netns: add and use net_ns

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DD000799C@AcuExch.aculab.com>
Date:   Fri, 2 Jun 2017 09:38:14 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Florian Westphal' <fw@...len.de>,
        "netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: RE: [PATCH nf-next] netns: add and use net_ns_barrier

From: Florian Westphal
> Sent: 30 May 2017 10:38
> 
> Quoting Joe Stringer:
>   If a user loads nf_conntrack_ftp, sends FTP traffic through a network
>   namespace, destroys that namespace then unloads the FTP helper module,
>   then the kernel will crash.
> 
> Events that lead to the crash:
> 1. conntrack is created with ftp helper in netns x
> 2. This netns is destroyed
> 3. netns destruction is scheduled
> 4. netns destruction wq starts, removes netns from global list
> 5. ftp helper is unloaded, which resets all helpers of the conntracks
> via for_each_net()
> 
> but because netns is already gone from list the for_each_net() loop
> doesn't include it, therefore all of these conntracks are unaffected.
> 
> 6. helper module unload finishes
> 7. netns wq invokes destructor for rmmod'ed helper
> 
...
>  void
>  nf_ct_iterate_destroy(int (*iter)(struct nf_conn *i, void *data), void *data)
> @@ -1734,6 +1736,13 @@ nf_ct_iterate_destroy(int (*iter)(struct nf_conn *i, void *data), void *data)
>  	}
>  	rtnl_unlock();
> 
> +	/* Need to wait for netns cleanup worker to finish, if its
> +	 * running -- it might have deleted a net namespace from
> +	 * the global list, so our __nf_ct_unconfirmed_destroy() might
> +	 * not have affected all namespaces.
> +	 */
> +	net_ns_barrier();
> +

A problem I see is that nothing obvious guarantees that the cleanup worker
has actually started.

	David