Subject: Re: [PATCH] netns: unix: only allow to find out unix socket in same net namespace

From: ebiederm-aS9lmoZGLiVWk0Htik3J/[email-masked] (Eric W. Biederman)
Date: Tue, 20 Aug 2013 22:30:50 -0700

Gao feng <[email-masked]> writes:

> Unix sockets are private resources of net namespace,
> allowing one net namespace to access to other netns's unix
> sockets is meaningless.

Allowing one net namespace to access another netns's unix socket is
deliberate behavior.  This is a desired and useful feature, and
only a misconfiguration of visible files would allow this to be a
problem.

> I'm researching a problem about shutdown from container,
> if the cotainer shares the same file /run/systemd/private
> with host, when we run shutdown -h xxx in container, the
> shutdown message will be send to the systemd-shutdownd
> through unix socket /run/systemd/private, and because
> systemd-shutdownd is running in host, so finally, the host
> will become shutdown.

The simple answer is don't do that then.  I can see no reason
to share /run outside of the container unless you want this kind of
behavior.

Quite frankly I want this behavior if I am using network namespaces
to support multiple routing contexts. That is if I am using scripts
like:

ip netns add other
ip netns exec other script

I don't want to have to remember to say 
ip netns orig exec shutdown -h now

There are more compelling uses and there is no cost in supporting this
in the kernel.

What kind of misconfiguration caused someone to complain about this?

> We should make sure unix sockets are per net namespace to
> avoid this problem.

Nacked-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/[email-masked]>

> Signed-off-by: Gao feng <[email-masked]>
> ---
>  net/unix/af_unix.c |  8 ++++++--
>  net/unix/diag.c    | 11 ++++++++---
>  2 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index c4ce243..98e3689 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -295,7 +295,8 @@ static inline struct sock *unix_find_socket_byname(struct net *net,
>  	return s;
>  }
>  
> -static struct sock *unix_find_socket_byinode(struct inode *i)
> +static struct sock *unix_find_socket_byinode(struct net *net,
> +					     struct inode *i)
>  {
>  	struct sock *s;
>  
> @@ -304,6 +305,9 @@ static struct sock *unix_find_socket_byinode(struct inode *i)
>  		    &unix_socket_table[i->i_ino & (UNIX_HASH_SIZE - 1)]) {
>  		struct dentry *dentry = unix_sk(s)->path.dentry;
>  
> +		if (!net_eq(sock_net(s), net))
> +			continue;
> +
>  		if (dentry && dentry->d_inode == i) {
>  			sock_hold(s);
>  			goto found;
> @@ -784,7 +788,7 @@ static struct sock *unix_find_other(struct net *net,
>  		err = -ECONNREFUSED;
>  		if (!S_ISSOCK(inode->i_mode))
>  			goto put_fail;
> -		u = unix_find_socket_byinode(inode);
> +		u = unix_find_socket_byinode(net, inode);
>  		if (!u)
>  			goto put_fail;
>  
> diff --git a/net/unix/diag.c b/net/unix/diag.c
> index d591091..80ada12 100644
> --- a/net/unix/diag.c
> +++ b/net/unix/diag.c
> @@ -218,20 +218,25 @@ done:
>  	return skb->len;
>  }
>  
> -static struct sock *unix_lookup_by_ino(int ino)
> +static struct sock *unix_lookup_by_ino(struct net *net, int ino)
>  {
>  	int i;
>  	struct sock *sk;
>  
>  	spin_lock(&unix_table_lock);
>  	for (i = 0; i < ARRAY_SIZE(unix_socket_table); i++) {
> -		sk_for_each(sk, &unix_socket_table[i])
> +		sk_for_each(sk, &unix_socket_table[i]) {
> +
> +			if (!net_eq(sock_net(sk), net))
> +				continue;
> +
>  			if (ino == sock_i_ino(sk)) {
>  				sock_hold(sk);
>  				spin_unlock(&unix_table_lock);
>  
>  				return sk;
>  			}
> +		}
>  	}
>  
>  	spin_unlock(&unix_table_lock);
> @@ -251,7 +256,7 @@ static int unix_diag_get_exact(struct sk_buff *in_skb,
>  	if (req->udiag_ino == 0)
>  		goto out_nosk;
>  
> -	sk = unix_lookup_by_ino(req->udiag_ino);
> +	sk = unix_lookup_by_ino(net, req->udiag_ino);
>  	err = -ENOENT;
>  	if (sk == NULL)
>  		goto out_nosk;