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Subject[PATCH 4.14 208/496] rds: Incorrect reference counting in TCP socket creation
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ka-Cheong Poon <ka-cheong.poon@oracle.com>

[ Upstream commit 84eef2b2187ed73c0e4520cbfeb874e964a0b56a ]

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

Fixes: 0933a578cd55 ("rds: tcp: use sock_create_lite() to create the accept socket")
Signed-off-by: Ka-Cheong Poon <ka-cheong.poon@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/rds/tcp_listen.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

--- 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 *so
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;

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