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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, kernel test robot <lkp@intel.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 3.18 17/24] llc: fix NULL pointer deref for SOCK_ZAPPED
Date:   Fri, 27 Apr 2018 15:57:52 +0200
Message-Id: <20180427135632.293874446@linuxfoundation.org>
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3.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Cong Wang <xiyou.wangcong@gmail.com>


[ Upstream commit 3a04ce7130a7e5dad4e78d45d50313747f8c830f ]

For SOCK_ZAPPED socket, we don't need to care about llc->sap,
so we should just skip these refcount functions in this case.

Fixes: f7e43672683b ("llc: hold llc_sap before release_sock()")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/llc/af_llc.c |   21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -187,7 +187,6 @@ static int llc_ui_release(struct socket
 {
 	struct sock *sk = sock->sk;
 	struct llc_sock *llc;
-	struct llc_sap *sap;
 
 	if (unlikely(sk == NULL))
 		goto out;
@@ -198,15 +197,19 @@ static int llc_ui_release(struct socket
 		llc->laddr.lsap, llc->daddr.lsap);
 	if (!llc_send_disc(sk))
 		llc_ui_wait_for_disc(sk, sk->sk_rcvtimeo);
-	sap = llc->sap;
-	/* Hold this for release_sock(), so that llc_backlog_rcv() could still
-	 * use it.
-	 */
-	llc_sap_hold(sap);
-	if (!sock_flag(sk, SOCK_ZAPPED))
+	if (!sock_flag(sk, SOCK_ZAPPED)) {
+		struct llc_sap *sap = llc->sap;
+
+		/* Hold this for release_sock(), so that llc_backlog_rcv()
+		 * could still use it.
+		 */
+		llc_sap_hold(sap);
 		llc_sap_remove_socket(llc->sap, sk);
-	release_sock(sk);
-	llc_sap_put(sap);
+		release_sock(sk);
+		llc_sap_put(sap);
+	} else {
+		release_sock(sk);
+	}
 	if (llc->dev)
 		dev_put(llc->dev);
 	sock_put(sk);