linux-kernel - [PATCH] User namespace: don't allow sysctl in non-init user ns

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Date:	Thu, 15 Sep 2011 14:48:12 -0500
From:	"Serge E. Hallyn" <serge.hallyn@...onical.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Containers <containers@...ts.osdl.org>,
	Andrew Morton <akpm@...l.org>,
	Vasiliy Kulikov <segoon@...nwall.com>, richard@....at
Subject: [PATCH] User namespace: don't allow sysctl in non-init user ns

sysctl.c has its own custom uid check, which is not user namespace
aware.  As discovered by Richard, that allows root in a container
privileged access to set all sysctls.

To fix that, just refuse access if current is not in init_user_ns.  We
may at some point want to relax that check so that some sysctls are
allowed - for instance dmesg_restrict when syslog is containerized.

Signed-off-by: Serge Hallyn <serge.hallyn@...onical.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: Vasiliy Kulikov <segoon@...nwall.com>
Cc: richard@....at
---
 kernel/sysctl.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 11d65b5..f2b42e2 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1697,6 +1697,8 @@ void register_sysctl_root(struct ctl_table_root *root)
 
 static int test_perm(int mode, int op)
 {
+	if (current_user_ns() != &init_user_ns)
+		return -EACCES;
 	if (!current_euid())
 		mode >>= 6;
 	else if (in_egroup_p(0))
-- 
1.7.5.4

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