Linux Ethernet Bridging - Dec 2015 - [Bridge] [PATCH net] bridge: Only call /sbin/bridge-stp for the initial network namespace

There is no defined mechanism to pass network namespace information
into /sbin/bridge-stp therefore don't even try to invoke it except
for bridge devices in the initial network namespace.

It is possible for unprivileged users to cause /sbin/bridge-stp to be
invoked for any network device name which if /sbin/bridge-stp does not
guard against unreasonable arguments or being invoked twice on the same
network device could cause problems.

Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
---
 net/bridge/br_stp_if.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 5396ff08af32..742fa89528ab 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -142,7 +142,9 @@ static void br_stp_start(struct net_bridge *br)
 	char *envp[] = { NULL };
 	struct net_bridge_port *p;
 
-	r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
+	r = -ENOENT;
+	if (dev_net(br->dev) == &init_net)
+		r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
 
 	spin_lock_bh(&br->lock);
 
-- 
2.2.1

On Mon, 30 Nov 2015 15:38:15 -0600
ebiederm at xmission.com (Eric W. Biederman) wrote:
> 
> There is no defined mechanism to pass network namespace information
> into /sbin/bridge-stp therefore don't even try to invoke it except
> for bridge devices in the initial network namespace.
> 
> It is possible for unprivileged users to cause /sbin/bridge-stp to be
> invoked for any network device name which if /sbin/bridge-stp does not
> guard against unreasonable arguments or being invoked twice on the same
> network device could cause problems.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm at
xmission.com>
> ---
>  net/bridge/br_stp_if.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 5396ff08af32..742fa89528ab 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -142,7 +142,9 @@ static void br_stp_start(struct net_bridge *br)
>  	char *envp[] = { NULL };
>  	struct net_bridge_port *p;
>  
> -	r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
> +	r = -ENOENT;
> +	if (dev_net(br->dev) == &init_net)
> +		r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
I don't think this will cause loud screams.
But it might break people that use containers to run virtual networks for
testing.

One coding nit:
Why are you afraid of using an else?

Am 30.11.2015 um 22:38 schrieb Eric W. Biederman:
> 
> There is no defined mechanism to pass network namespace information
> into /sbin/bridge-stp therefore don't even try to invoke it except
> for bridge devices in the initial network namespace.
> 
> It is possible for unprivileged users to cause /sbin/bridge-stp to be
> invoked for any network device name which if /sbin/bridge-stp does not
> guard against unreasonable arguments or being invoked twice on the same
> network device could cause problems.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm at
xmission.com>
Just figured that /sbin/bridge-stp is a shell script.
Network interfaces can contain a lot of funny characters,
maybe this is after all a security issue.

Thanks,
//richard

On Mon, Nov 30, 2015, at 22:38, Eric W. Biederman wrote:
> Signed-off-by: "Eric W. Biederman" <ebiederm at
xmission.com>
> ---
>  net/bridge/br_stp_if.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
> index 5396ff08af32..742fa89528ab 100644
> --- a/net/bridge/br_stp_if.c
> +++ b/net/bridge/br_stp_if.c
> @@ -142,7 +142,9 @@ static void br_stp_start(struct net_bridge *br)
>  	char *envp[] = { NULL };
>  	struct net_bridge_port *p;
>  
> -       r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
> +       r = -ENOENT;
> +       if (dev_net(br->dev) == &init_net)
net_eq ?
> +               r = call_usermodehelper(BR_STP_PROG, argv, envp,
> UMH_WAIT_PROC);
>  
>  	spin_lock_bh(&br->lock);
>  
Otherwise, ack, so far.

As our /sys interfaces directories are tagged by the net namespace it
would actually make sense to run bridge-stp automatically in another
name space.

Bye,
Hannes

From: ebiederm at xmission.com (Eric W. Biederman)
Date: Mon, 30 Nov 2015 15:38:15 -0600
> +	if (dev_net(br->dev) == &init_net)
Please respin this using net_eq() as Hannes pointed out.

Thanks.