[I stole this patch from Eric Biederman. He 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.

[Hannes: changed patch using netns_eq]

Cc: Eric W. Biederman <redacted>
Signed-off-by: Eric W. Biederman <redacted>
Signed-off-by: Hannes Frederic Sowa <redacted>
---
 net/bridge/br_stp_if.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 905cedd37a0539..a31ac6ad76a223 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c

@@ -143,7 +143,10 @@ 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);
+	if (net_eq(dev_net(br->dev), &init_net))
+		r = call_usermodehelper(BR_STP_PROG, argv, envp, UMH_WAIT_PROC);
+	else
+		r = -ENOENT;
 
 	spin_lock_bh(&br->lock);
 

-- 
2.5.0