linux-kernel - [PATCH 2/2] net: Use ns_capable_noaudit() when determining net sysctl permissions

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Message-Id: <1462575854-4301-3-git-send-email-tyhicks@canonical.com>
Date:	Fri,  6 May 2016 18:04:14 -0500
From:	Tyler Hicks <tyhicks@...onical.com>
To:	linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	"David S . Miller" <davem@...emloft.net>
Subject: [PATCH 2/2] net: Use ns_capable_noaudit() when determining net sysctl permissions

The capability check should not be audited since it is only being used
to determine the inode permissions. A failed check does not indicate a
violation of security policy but, when an LSM is enabled, a denial audit
message was being generated.

The denial audit message caused confusion for some application authors
because root-running Go applications always triggered the denial. To
prevent this confusion, the capability check in net_ctl_permissions() is
switched to the noaudit variant.

BugLink: https://launchpad.net/bugs/1465724

Signed-off-by: Tyler Hicks <tyhicks@...onical.com>
---
 net/sysctl_net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sysctl_net.c b/net/sysctl_net.c
index ed98c1f..46a71c7 100644
--- a/net/sysctl_net.c
+++ b/net/sysctl_net.c
@@ -46,7 +46,7 @@ static int net_ctl_permissions(struct ctl_table_header *head,
 	kgid_t root_gid = make_kgid(net->user_ns, 0);
 
 	/* Allow network administrator to have same access as root. */
-	if (ns_capable(net->user_ns, CAP_NET_ADMIN) ||
+	if (ns_capable_noaudit(net->user_ns, CAP_NET_ADMIN) ||
 	    uid_eq(root_uid, current_euid())) {
 		int mode = (table->mode >> 6) & 7;
 		return (mode << 6) | (mode << 3) | mode;
-- 
2.7.4