linux-kernel - [PATCH][next] mptcp: fix a dereference of pointer before msk is null checked.

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Date:   Mon,  9 Nov 2020 12:52:15 +0000
From:   Colin King <colin.king@...onical.com>
To:     Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Geliang Tang <geliangtang@...il.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        mptcp@...ts.01.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][next] mptcp: fix a dereference of pointer before msk is null checked.

From: Colin Ian King <colin.king@...onical.com>

Currently the assignment of pointer net from the sock_net(sk) call
is potentially dereferencing a null pointer sk. sk points to the
same location as pointer msk and msk is being null checked after
the sock_net call.  Fix this by calling sock_net after the null
check on pointer msk.

Addresses-Coverity: ("Dereference before null check")
Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 net/mptcp/pm_netlink.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index ed60538df7b2..e76879ea5a30 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -206,13 +206,15 @@ static void mptcp_pm_add_timer(struct timer_list *timer)
 	struct mptcp_pm_add_entry *entry = from_timer(entry, timer, add_timer);
 	struct mptcp_sock *msk = entry->sock;
 	struct sock *sk = (struct sock *)msk;
-	struct net *net = sock_net(sk);
+	struct net *net;
 
 	pr_debug("msk=%p", msk);
 
 	if (!msk)
 		return;
 
+	net = sock_net(sk);
+
 	if (inet_sk_state_load(sk) == TCP_CLOSE)
 		return;
 
-- 
2.28.0