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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Lin Zhang <xiaolou4617@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.9 117/310] net: llc: add lock_sock in llc_ui_bind to avoid a race condition
Date:   Wed, 11 Apr 2018 20:34:16 +0200
Message-Id: <20180411183627.204637839@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: linzhang <xiaolou4617@gmail.com>


[ Upstream commit 0908cf4dfef35fc6ac12329007052ebe93ff1081 ]

There is a race condition in llc_ui_bind if two or more processes/threads
try to bind a same socket.

If more processes/threads bind a same socket success that will lead to
two problems, one is this action is not what we expected, another is
will lead to kernel in unstable status or oops(in my simple test case,
cause llc2.ko can't unload).

The current code is test SOCK_ZAPPED bit to avoid a process to
bind a same socket twice but that is can't avoid more processes/threads
try to bind a same socket at the same time.

So, add lock_sock in llc_ui_bind like others, such as llc_ui_connect.

Signed-off-by: Lin Zhang <xiaolou4617@gmail.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/llc/af_llc.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -309,6 +309,8 @@ static int llc_ui_bind(struct socket *so
 	int rc = -EINVAL;
 
 	dprintk("%s: binding %02X\n", __func__, addr->sllc_sap);
+
+	lock_sock(sk);
 	if (unlikely(!sock_flag(sk, SOCK_ZAPPED) || addrlen != sizeof(*addr)))
 		goto out;
 	rc = -EAFNOSUPPORT;
@@ -380,6 +382,7 @@ static int llc_ui_bind(struct socket *so
 out_put:
 	llc_sap_put(sap);
 out:
+	release_sock(sk);
 	return rc;
 }