netdev - [PATCH][next] mptcp: Avoid NULL dereference in mptcp_getsockopt_subflow

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Date:   Mon, 20 Sep 2021 09:42:32 -0600
From:   Tim Gardner <tim.gardner@...onical.com>
To:     mptcp@...ts.linux.dev
Cc:     tim.gardner@...onical.com,
        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>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH][next] mptcp: Avoid NULL dereference in mptcp_getsockopt_subflow_addrs()

Coverity complains of a possible NULL dereference in
mptcp_getsockopt_subflow_addrs():

861        } else if (sk->sk_family == AF_INET6) {
    	3. returned_null: inet6_sk returns NULL. [show details]
    	4. var_assigned: Assigning: np = NULL return value from inet6_sk.
 862                const struct ipv6_pinfo *np = inet6_sk(sk);

Fix this by checking for NULL.

Cc: Mat Martineau <mathew.j.martineau@...ux.intel.com>
Cc: Matthieu Baerts <matthieu.baerts@...sares.net>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org
Cc: mptcp@...ts.linux.dev
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Tim Gardner <tim.gardner@...onical.com>

[ I'm not at all sure this is the right thing to do since the final result is to
return garbage to user space in mptcp_getsockopt_subflow_addrs(). Is this one
of those cases where inet6_sk() can't fail ?]
---
 net/mptcp/sockopt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 8137cc3a4296..c89f2bedce79 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -861,6 +861,9 @@ static void mptcp_get_sub_addrs(const struct sock *sk, struct mptcp_subflow_addr
 	} else if (sk->sk_family == AF_INET6) {
 		const struct ipv6_pinfo *np = inet6_sk(sk);
 
+		if (!np)
+			return;
+
 		a->sin6_local.sin6_family = AF_INET6;
 		a->sin6_local.sin6_port = inet->inet_sport;
 
-- 
2.33.0