Commit 0933a578cd55 ("rds: tcp: use sock_create_lite() to create the
accept socket") has a reference counting issue in TCP socket creation
when accepting a new connection. The code uses sock_create_lite() to
create a kernel socket. But it does not do __module_get() on the
socket owner. When the connection is shutdown and sock_release() is
called to free the socket, the owner's reference count is decremented
and becomes incorrect. Note that this bug only shows up when the socket
owner is configured as a kernel module.
v2: Update comments
Signed-off-by: Ka-Cheong Poon <ka-cheong.p...@oracle.com>
---
net/rds/tcp_listen.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index c061d6e..2257118 100644
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2006 Oracle. All rights reserved.
+ * Copyright (c) 2006, 2018 Oracle. All rights reserved.
*
* This software is available to you under a choice of one of two
* licenses. You may choose to be licensed under the terms of the GNU
@@ -142,12 +142,20 @@ int rds_tcp_accept_one(struct socket *sock)
if (ret)
goto out;
- new_sock->type = sock->type;
- new_sock->ops = sock->ops;
ret = sock->ops->accept(sock, new_sock, O_NONBLOCK, true);
if (ret < 0)
goto out;
+ /* sock_create_lite() does not get a hold on the owner module so we
+ * need to do it here. Note that sock_release() uses sock->ops to
+ * determine if it needs to decrement the reference count. So set
+ * sock->ops after calling accept() in case that fails. And there's
+ * no need to do try_module_get() as the listener should have a hold
+ * already.
+ */
+ new_sock->ops = sock->ops;
+ __module_get(new_sock->ops->owner);
+
ret = rds_tcp_keepalive(new_sock);
if (ret < 0)
goto out;
--
1.8.3.1
