tipc: fix netns refcnt leak

When the TIPC module is loaded, we launch a topology server in kernel
space, which in its turn is creating TIPC sockets for communication
with topology server users. Because both the socket's creator and
provider reside in the same module, it is necessary that the TIPC
module's reference count remains zero after the server is started and
the socket created; otherwise it becomes impossible to perform "rmmod"
even on an idle module.

Currently, we achieve this by defining a separate "tipc_proto_kern"
protocol struct, that is used only for kernel space socket allocations.
This structure has the "owner" field set to NULL, which restricts the
module reference count from being be bumped when sk_alloc() for local
sockets is called. Furthermore, we have defined three kernel-specific
functions, tipc_sock_create_local(), tipc_sock_release_local() and
tipc_sock_accept_local(), to avoid the module counter being modified
when module local sockets are created or deleted. This has worked well
until we introduced name space support.

However, after name space support was introduced, we have observed that
a reference count leak occurs, because the netns counter is not
decremented in tipc_sock_delete_local().

This commit remedies this problem. But instead of just modifying
tipc_sock_delete_local(), we eliminate the whole parallel socket
handling infrastructure, and start using the regular sk_create_kern(),
kernel_accept() and sk_release_kernel() calls. Since those functions
manipulate the module counter, we must now compensate for that by
explicitly decrementing the counter after module local sockets are
created, and increment it just before calling sk_release_kernel().

Fixes: a62fbccecd62 ("tipc: make subscriber server support net namespace")
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Jon Maloy <jon.maloy@ericson.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Reported-by: Cong Wang <cwang@twopensource.com>
Tested-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 82 deletions

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 934947f038b6..813847d25a49 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -121,9 +121,7 @@ static int __tipc_sendmsg(struct socket *sock, struct msghdr *m, size_t dsz);
 static const struct proto_ops packet_ops;
 static const struct proto_ops stream_ops;
 static const struct proto_ops msg_ops;
-
 static struct proto tipc_proto;
-static struct proto tipc_proto_kern;
 
 static const struct nla_policy tipc_nl_sock_policy[TIPC_NLA_SOCK_MAX + 1] = {
 	[TIPC_NLA_SOCK_UNSPEC]		= { .type = NLA_UNSPEC },
@@ -341,11 +339,7 @@ static int tipc_sk_create(struct net *net, struct socket *sock,
 	}
 
 	/* Allocate socket's protocol area */
-	if (!kern)
-		sk = sk_alloc(net, AF_TIPC, GFP_KERNEL, &tipc_proto);
-	else
-		sk = sk_alloc(net, AF_TIPC, GFP_KERNEL, &tipc_proto_kern);
-
+	sk = sk_alloc(net, AF_TIPC, GFP_KERNEL, &tipc_proto);
 	if (sk == NULL)
 		return -ENOMEM;
 
@@ -383,75 +377,6 @@ static int tipc_sk_create(struct net *net, struct socket *sock,
 	return 0;
 }
 
-/**
- * tipc_sock_create_local - create TIPC socket from inside TIPC module
- * @type: socket type - SOCK_RDM or SOCK_SEQPACKET
- *
- * We cannot use sock_creat_kern here because it bumps module user count.
- * Since socket owner and creator is the same module we must make sure
- * that module count remains zero for module local sockets, otherwise
- * we cannot do rmmod.
- *
- * Returns 0 on success, errno otherwise
- */
-int tipc_sock_create_local(struct net *net, int type, struct socket **res)
-{
-	int rc;
-
-	rc = sock_create_lite(AF_TIPC, type, 0, res);
-	if (rc < 0) {
-		pr_err("Failed to create kernel socket\n");
-		return rc;
-	}
-	tipc_sk_create(net, *res, 0, 1);
-
-	return 0;
-}
-
-/**
- * tipc_sock_release_local - release socket created by tipc_sock_create_local
- * @sock: the socket to be released.
- *
- * Module reference count is not incremented when such sockets are created,
- * so we must keep it from being decremented when they are released.
- */
-void tipc_sock_release_local(struct socket *sock)
-{
-	tipc_release(sock);
-	sock->ops = NULL;
-	sock_release(sock);
-}
-
-/**
- * tipc_sock_accept_local - accept a connection on a socket created
- * with tipc_sock_create_local. Use this function to avoid that
- * module reference count is inadvertently incremented.
- *
- * @sock:    the accepting socket
- * @newsock: reference to the new socket to be created
- * @flags:   socket flags
- */
-
-int tipc_sock_accept_local(struct socket *sock, struct socket **newsock,
-			   int flags)
-{
-	struct sock *sk = sock->sk;
-	int ret;
-
-	ret = sock_create_lite(sk->sk_family, sk->sk_type,
-			       sk->sk_protocol, newsock);
-	if (ret < 0)
-		return ret;
-
-	ret = tipc_accept(sock, *newsock, flags);
-	if (ret < 0) {
-		sock_release(*newsock);
-		return ret;
-	}
-	(*newsock)->ops = sock->ops;
-	return ret;
-}
-
 static void tipc_sk_callback(struct rcu_head *head)
 {
 	struct tipc_sock *tsk = container_of(head, struct tipc_sock, rcu);
@@ -2608,12 +2533,6 @@ static struct proto tipc_proto = {
 	.sysctl_rmem	= sysctl_tipc_rmem
 };
 
-static struct proto tipc_proto_kern = {
-	.name		= "TIPC",
-	.obj_size	= sizeof(struct tipc_sock),
-	.sysctl_rmem	= sysctl_tipc_rmem
-};
-
 /**
  * tipc_socket_init - initialize TIPC socket interface
  *