The TUN driver lacks any LSM hooks which makes it difficult for LSM modules,
such as SELinux, to enforce access controls on network traffic generated by
TUN users; this is particularly problematic for virtualization apps such as
QEMU and KVM. This patch adds three new LSM hooks designed to control the
creation and attachment of TUN devices, the hooks are:
* security_tun_dev_create()
Provides access control for the creation of new TUN devices
* security_tun_dev_post_create()
Provides the ability to create the necessary socket LSM state for newly
created TUN devices
* security_tun_dev_attach()
Provides access control for attaching to existing, persistent TUN devices
and the ability to update the TUN device's socket LSM state as necessary
---
drivers/net/tun.c | 41 +++++++++++++++++++++++------------------
include/linux/security.h | 34 ++++++++++++++++++++++++++++++++++
security/commoncap.c | 26 ++++++++++++++++++++++++++
security/security.c | 18 ++++++++++++++++++
4 files changed, 101 insertions(+), 18 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 027f7ab..f26c1fe 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -130,28 +130,22 @@ static inline struct tun_sock *tun_sk(struct sock *sk)
static int tun_attach(struct tun_struct *tun, struct file *file)
{
struct tun_file *tfile = file->private_data;
- const struct cred *cred = current_cred();
- int err;
+ int err = 0;
ASSERT_RTNL();
- /* Check permissions */
- if (((tun->owner != -1 && cred->euid != tun->owner) ||
- (tun->group != -1 && !in_egroup_p(tun->group))) &&
- !capable(CAP_NET_ADMIN))
- return -EPERM;
-
netif_tx_lock_bh(tun->dev);
- err = -EINVAL;
- if (tfile->tun)
+ if (tfile->tun) {
+ err = -EINVAL;
goto out;
+ }
- err = -EBUSY;
- if (tun->tfile)
+ if (tun->tfile) {
+ err = -EBUSY;
goto out;
+ }
- err = 0;
tfile->tun = tun;
tun->tfile = tfile;
dev_hold(tun->dev);
@@ -922,6 +916,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
struct sock *sk;
struct tun_struct *tun;
struct net_device *dev;
+ const struct cred *cred = current_cred();
int err;
dev = __dev_get_by_name(net, ifr->ifr_name);
@@ -935,6 +930,13 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
else
return -EINVAL;
+ if ((tun->owner != -1 && cred->euid != tun->owner) ||
+ (tun->group != -1 && !in_egroup_p(tun->group)))
+ return -EPERM;
+ err = security_tun_dev_attach(tun->sk);
+ if (err < 0)
+ return err;
+
err = tun_attach(tun, file);
if (err < 0)
return err;
@@ -943,10 +945,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
char *name;
unsigned long flags = 0;
- err = -EINVAL;
-
- if (!capable(CAP_NET_ADMIN))
- return -EPERM;
+ err = security_tun_dev_create();
+ if (err < 0)
+ return err;
/* Set dev type */
if (ifr->ifr_flags & IFF_TUN) {
@@ -957,8 +958,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
/* TAP device */
flags |= TUN_TAP_DEV;
name = "tap%d";
- } else
+ } else {
+ err = -EINVAL;
goto failed;
+ }
if (*ifr->ifr_name)
name = ifr->ifr_name;
@@ -989,6 +992,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
tun->sk = sk;
container_of(sk, struct tun_sock, sk)->tun = tun;
+ security_tun_dev_post_create(sk);
+
tun_net_init(dev);
if (strchr(dev->name, '%')) {
diff --git a/include/linux/security.h b/include/linux/security.h
index 5eff459..67f5d91 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -91,6 +91,9 @@ struct seq_file;
extern int cap_netlink_send(struct sock *sk, struct sk_buff *skb);
extern int cap_netlink_recv(struct sk_buff *skb, int cap);
+extern int cap_tun_dev_create(void);
+extern int cap_tun_dev_attach(void);
+
extern unsigned long mmap_min_addr;
/*
* Values used in the task_security_ops calls
@@ -974,6 +977,17 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
* Sets the connection's peersid to the secmark on skb.
* @req_classify_flow:
* Sets the flow's sid to the openreq sid.
+ * @tun_dev_create:
+ * Check permissions prior to creating a new TUN device.
+ * @tun_dev_post_create:
+ * This hook allows a module to update or allocate a per-socket security
+ * structure.
+ * @tun_sk contains the newly created sock structure.
+ * @tun_dev_attach:
+ * Check permissions prior to attaching to a persistent TUN device. This
+ * hook can also be used by the module to update any security state
+ * associated with the TUN device's sock structure.
+ * @tun_sk contains the existing sock structure.
*
* Security hooks for XFRM operations.
*
@@ -1572,6 +1586,9 @@ struct security_operations {
void (*inet_csk_clone) (struct sock *newsk, const struct request_sock *req);
void (*inet_conn_established) (struct sock *sk, struct sk_buff *skb);
void (*req_classify_flow) (const struct request_sock *req, struct flowi *fl);
+ int (*tun_dev_create)(void);
+ void (*tun_dev_post_create)(struct sock *tun_sk);
+ int (*tun_dev_attach)(struct sock *tun_sk);
#endif /* CONFIG_SECURITY_NETWORK */
#ifdef CONFIG_SECURITY_NETWORK_XFRM
@@ -2557,6 +2574,9 @@ void security_inet_csk_clone(struct sock *newsk,
const struct request_sock *req);
void security_inet_conn_established(struct sock *sk,
struct sk_buff *skb);
+int security_tun_dev_create(void);
+void security_tun_dev_post_create(struct sock *tun_sk);
+int security_tun_dev_attach(struct sock *tun_sk);
#else /* CONFIG_SECURITY_NETWORK */
static inline int security_unix_stream_connect(struct socket *sock,
@@ -2707,6 +2727,20 @@ static inline void security_inet_conn_established(struct sock *sk,
struct sk_buff *skb)
{
}
+
+static inline int security_tun_dev_create(void)
+{
+ return cap_tun_dev_create();
+}
+
+static inline void security_tun_dev_post_create(struct sock *tun_sk)
+{
+}
+
+static inline int security_tun_dev_attach(struct sock *tun_sk)
+{
+ return cap_tun_dev_attach();
+}
#endif /* CONFIG_SECURITY_NETWORK */
#ifdef CONFIG_SECURITY_NETWORK_XFRM
diff --git a/security/commoncap.c b/security/commoncap.c
index 48b7e02..07125a6 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -984,3 +984,29 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
cap_sys_admin = 1;
return __vm_enough_memory(mm, pages, cap_sys_admin);
}
+
+/**
+ * cap_tun_dev_create - Determine if creation of a new TUN device is allowed
+ *
+ * Determine if the user is allowed to create a new TUN device, historically
+ * this has always required the CAP_NET_ADMIN permission.
+ */
+int cap_tun_dev_create(void)
+{
+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+ return 0;
+}
+
+/**
+ * cap_tun_dev_attach - Determine if attaching to an TUN device is allowed
+ *
+ * Determine if the user is allowed to attach to an existing persistent TUN
+ * device, historically this has always required the CAP_NET_ADMIN permission.
+ */
+int cap_tun_dev_attach(void)
+{
+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+ return 0;
+}
diff --git a/security/security.c b/security/security.c
index dc7674f..14ebf82 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1112,6 +1112,24 @@ void security_inet_conn_established(struct sock *sk,
security_ops->inet_conn_established(sk, skb);
}
+int security_tun_dev_create(void)
+{
+ return security_ops->tun_dev_create();
+}
+EXPORT_SYMBOL(security_tun_dev_create);
+
+void security_tun_dev_post_create(struct sock *tun_sk)
+{
+ return security_ops->tun_dev_post_create(tun_sk);
+}
+EXPORT_SYMBOL(security_tun_dev_post_create);
+
+int security_tun_dev_attach(struct sock *tun_sk)
+{
+ return security_ops->tun_dev_attach(tun_sk);
+}
+EXPORT_SYMBOL(security_tun_dev_attach);
+
#endif /* CONFIG_SECURITY_NETWORK */
#ifdef CONFIG_SECURITY_NETWORK_XFRM
--
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