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[PATCH net] bridge: Only call /sbin/bridge-stp for the initial network namespace

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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@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

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user controllable usermodehelper in br_stp_if.c Richard Weinberger <richard@nod.at> - 2015-11-29 23:50 +0100
  Re: user controllable usermodehelper in br_stp_if.c Kees Cook <keescook@chromium.org> - 2015-11-30 21:20 +0100
    [PATCH net] bridge: Only call /sbin/bridge-stp for the initial network namespace ebiederm@xmission.com (Eric W. Biederman) - 2015-11-30 23:00 +0100
      Re: [PATCH net] bridge: Only call /sbin/bridge-stp for the initial  network namespace Stephen Hemminger <stephen@networkplumber.org> - 2015-11-30 23:20 +0100
        Re: [PATCH net] bridge: Only call /sbin/bridge-stp for the initial network namespace ebiederm@xmission.com (Eric W. Biederman) - 2015-11-30 23:30 +0100
      Re: [PATCH net] bridge: Only call /sbin/bridge-stp for the initial  network namespace Richard Weinberger <richard@nod.at> - 2015-12-01 00:00 +0100
      Re: [PATCH net] bridge: Only call /sbin/bridge-stp for the initial  network namespace Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-12-01 15:20 +0100
      Re: [PATCH net] bridge: Only call /sbin/bridge-stp for the initial  network namespace David Miller <davem@davemloft.net> - 2015-12-03 06:00 +0100
        Re: [PATCH net] bridge: Only call /sbin/bridge-stp for the initial  network namespace Kees Cook <keescook@chromium.org> - 2015-12-08 22:00 +0100
    Re: user controllable usermodehelper in br_stp_if.c Richard Weinberger <richard@nod.at> - 2015-12-01 00:10 +0100

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