Subject: Re: [PATCH 1/3] IPVS: Change of socket usage to enable name space exit.

From: [email-masked] (Eric W. Biederman)
Date: Wed, 20 Apr 2011 02:40:09 -0700

Hans Schillstrom <[email-masked]> writes:

> This is the first patch in a series of three.
> The cleanup doesn't work when not exit in a clean way by using ipvsadm.
> Killing of a namespace causes a hanging ipvs, this series will cure that.
>
> If the sync daemons run in a namespace while it crashes
> or get killed, there is no way to stop them except for a reboot.
>
> Kernel threads should not increment the use count of a socket.
> By calling sk_change_net() after creating a socket this is avoided.
> sock_release cant be used, instead sk_release_kernel() should be used.
>
> Thanks to Eric W Biederman.
>
> This patch is based on net-next-2.6  ver 2.6.39-rc2

I am not comfortable with this patch on it's own.  What kills the
daemons on network namespace exit?

I would be a little happier if the code also used sock_create_kern
instead of __sock_create. Now that it uses sk_change_net.  Just to make
the code more idiomatic.

But not actually guaranteeing that the namespace exit kills the threads
at this point seems pretty badly broken, as this idiom is not safe
unless we have a hard guarantee that the threads are dead.

Eric

> Signed-off-by: Hans Schillstrom <[email-masked]>
> ---
>  net/netfilter/ipvs/ip_vs_sync.c |   28 +++++++++++++++++++---------
>  1 files changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/net/netfilter/ipvs/ip_vs_sync.c b/net/netfilter/ipvs/ip_vs_sync.c
> index 3e7961e..3f87555 100644
> --- a/net/netfilter/ipvs/ip_vs_sync.c
> +++ b/net/netfilter/ipvs/ip_vs_sync.c
> @@ -1309,7 +1309,12 @@ static struct socket *make_send_sock(struct net *net)
>  		pr_err("Error during creation of socket; terminating\n");
>  		return ERR_PTR(result);
>  	}
> -
> +	/*
> +	 * Kernel sockets that are a part of a namespace, should not
> +	 * hold a reference to a namespace in order to allow to stop it.
> +	 * After sk_change_net should be released using sk_release_kernel.
> +	 */
> +	sk_change_net(sock->sk, net);
>  	result = set_mcast_if(sock->sk, ipvs->master_mcast_ifn);
>  	if (result < 0) {
>  		pr_err("Error setting outbound mcast interface\n");
> @@ -1334,8 +1339,8 @@ static struct socket *make_send_sock(struct net *net)
>
>  	return sock;
>
> -  error:
> -	sock_release(sock);
> +error:
> +	sk_release_kernel(sock->sk);
>  	return ERR_PTR(result);
>  }
>
> @@ -1355,7 +1360,12 @@ static struct socket *make_receive_sock(struct net *net)
>  		pr_err("Error during creation of socket; terminating\n");
>  		return ERR_PTR(result);
>  	}
> -
> +	/*
> +	 * Kernel sockets that are a part of a namespace, should not
> +	 * hold a reference to a namespace in order to allow to stop it.
> +	 * After sk_change_net should be released using sk_release_kernel.
> +	 */
> +	sk_change_net(sock->sk, net);
>  	/* it is equivalent to the REUSEADDR option in user-space */
>  	sock->sk->sk_reuse = 1;
>
> @@ -1377,8 +1387,8 @@ static struct socket *make_receive_sock(struct net *net)
>
>  	return sock;
>
> -  error:
> -	sock_release(sock);
> +error:
> +	sk_release_kernel(sock->sk);
>  	return ERR_PTR(result);
>  }
>
> @@ -1473,7 +1483,7 @@ static int sync_thread_master(void *data)
>  		ip_vs_sync_buff_release(sb);
>
>  	/* release the sending multicast socket */
> -	sock_release(tinfo->sock);
> +	sk_release_kernel(tinfo->sock->sk);
>  	kfree(tinfo);
>
>  	return 0;
> @@ -1513,7 +1523,7 @@ static int sync_thread_backup(void *data)
>  	}
>
>  	/* release the sending multicast socket */
> -	sock_release(tinfo->sock);
> +	sk_release_kernel(tinfo->sock->sk);
>  	kfree(tinfo->buf);
>  	kfree(tinfo);
>
> @@ -1601,7 +1611,7 @@ outtinfo:
>  outbuf:
>  	kfree(buf);
>  outsocket:
> -	sock_release(sock);
> +	sk_release_kernel(sock->sk);
>  out:
>  	return result;
>  }
> --
> 1.7.2.3