MPTCP sockets created via accept() inherit their LSM label
from the initial request socket, which in turn get it from the
listener socket's first subflow. The latter is a kernel socket,
and get the relevant labeling at creation time.
Due to all the above even the accepted MPTCP socket get a kernel
label, causing unexpected behaviour and failure on later LSM tests.
Address the issue factoring out a socket creation helper that does
not include the post-creation LSM checks. Use such helper to create
mptcp subflow as in-kernel sockets and doing explicitly LSM validation:
vs the current user for the first subflow, as a kernel socket otherwise.
Fixes: 0c14846032f2 ("mptcp: fix security context on server socket")
Reported-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
---
include/linux/net.h | 2 ++
net/mptcp/subflow.c | 19 ++++++++++++--
net/socket.c | 60 ++++++++++++++++++++++++++++++---------------
3 files changed, 59 insertions(+), 22 deletions(-)
diff --git a/include/linux/net.h b/include/linux/net.h
index b73ad8e3c212..91713012504d 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -251,6 +251,8 @@ int sock_wake_async(struct socket_wq *sk_wq, int how, int band);
int sock_register(const struct net_proto_family *fam);
void sock_unregister(int family);
bool sock_is_registered(int family);
+int __sock_create_nosec(struct net *net, int family, int type, int proto,
+ struct socket **res, int kern);
int __sock_create(struct net *net, int family, int type, int proto,
struct socket **res, int kern);
int sock_create(int family, int type, int proto, struct socket **res);
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index d5ff502c88d7..e7e6f17df7ef 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1646,11 +1646,26 @@ int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
if (unlikely(!sk->sk_socket))
return -EINVAL;
- err = sock_create_kern(net, sk->sk_family, SOCK_STREAM, IPPROTO_TCP,
- &sf);
+ /* the subflow is created by the kernel, and we need kernel annotation
+ * for lockdep's sake...
+ */
+ err = __sock_create_nosec(net, sk->sk_family, SOCK_STREAM, IPPROTO_TCP,
+ &sf, 1);
if (err)
return err;
+ /* ... but the MPC subflow will be indirectly exposed to the
+ * user-space via accept(). Let's attach the current user security
+ * label to the first subflow, that is when msk->first is not yet
+ * initialized.
+ */
+ err = security_socket_post_create(sf, sk->sk_family, SOCK_STREAM,
+ IPPROTO_TCP, !!mptcp_sk(sk)->first);
+ if (err) {
+ sock_release(sf);
+ return err;
+ }
+
lock_sock(sf->sk);
/* the newly created socket has to be in the same cgroup as its parent */
diff --git a/net/socket.c b/net/socket.c
index 55c5d536e5f6..d5d51e4e26ae 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1426,23 +1426,11 @@ int sock_wake_async(struct socket_wq *wq, int how, int band)
}
EXPORT_SYMBOL(sock_wake_async);
-/**
- * __sock_create - creates a socket
- * @net: net namespace
- * @family: protocol family (AF_INET, ...)
- * @type: communication type (SOCK_STREAM, ...)
- * @protocol: protocol (0, ...)
- * @res: new socket
- * @kern: boolean for kernel space sockets
- *
- * Creates a new socket and assigns it to @res, passing through LSM.
- * Returns 0 or an error. On failure @res is set to %NULL. @kern must
- * be set to true if the socket resides in kernel space.
- * This function internally uses GFP_KERNEL.
- */
-int __sock_create(struct net *net, int family, int type, int protocol,
- struct socket **res, int kern)
+
+/*creates a socket leaving LSM post-creation checks to the caller */
+int __sock_create_nosec(struct net *net, int family, int type, int protocol,
+ struct socket **res, int kern)
{
int err;
struct socket *sock;
@@ -1528,11 +1516,8 @@ int __sock_create(struct net *net, int family, int type, int protocol,
* module can have its refcnt decremented
*/
module_put(pf->owner);
- err = security_socket_post_create(sock, family, type, protocol, kern);
- if (err)
- goto out_sock_release;
- *res = sock;
+ *res = sock;
return 0;
out_module_busy:
@@ -1548,6 +1533,41 @@ int __sock_create(struct net *net, int family, int type, int protocol,
rcu_read_unlock();
goto out_sock_release;
}
+
+/**
+ * __sock_create - creates a socket
+ * @net: net namespace
+ * @family: protocol family (AF_INET, ...)
+ * @type: communication type (SOCK_STREAM, ...)
+ * @protocol: protocol (0, ...)
+ * @res: new socket
+ * @kern: boolean for kernel space sockets
+ *
+ * Creates a new socket and assigns it to @res, passing through LSM.
+ * Returns 0 or an error. On failure @res is set to %NULL. @kern must
+ * be set to true if the socket resides in kernel space.
+ * This function internally uses GFP_KERNEL.
+ */
+
+int __sock_create(struct net *net, int family, int type, int protocol,
+ struct socket **res, int kern)
+{
+ struct socket *sock;
+ int err;
+
+ err = __sock_create_nosec(net, family, type, protocol, &sock, kern);
+ if (err)
+ return err;
+
+ err = security_socket_post_create(sock, family, type, protocol, kern);
+ if (err) {
+ sock_release(sock);
+ return err;
+ }
+
+ *res = sock;
+ return 0;
+}
EXPORT_SYMBOL(__sock_create);
/**
--
2.38.1
