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

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Date:	Mon, 30 Nov 2015 15:38:15 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Miller <davem@...emloft.net>
Cc:	Richard Weinberger <richard@....at>,
	"netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"kernel-hardening\@lists.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	bridge@...ts.linux-foundation.org,
	Stephen Hemminger <stephen@...workplumber.org>,
	Kees Cook <keescook@...omium.org>
Subject: [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@...ssion.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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