netdev - [PATCH net] tcp: do not inherit mc

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Date:   Tue, 09 May 2017 05:17:15 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>, Pray3r <pray3r.z@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH net] tcp: do not inherit mc_list from parent

From: Eric Dumazet <edumazet@...gle.com>

syzkaller found a way to trigger double frees from ip_mc_drop_socket()

It turns out that leave a copy of parent mc_list at accept() time,
which is very bad.

Very similar to commit 8b485ce69876 ("tcp: do not inherit
fastopen_req from parent")

Initial report from Pray3r, completed by Andrey one.
Thanks a lot to them !

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Pray3r <pray3r.z@...il.com>
Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
---
Notes:
 - day-0 bug.
 - Not sure if it makes sense for TCP socket to be able to join MC
group ?

 net/ipv4/tcp_minisocks.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 717be4de53248352c758b50557987d898340dd4f..03035e2857fc8b6e4cd8af6e46e81048d4de9105 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -448,6 +448,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 		minmax_reset(&newtp->rtt_min, tcp_time_stamp, ~0U);
 		newicsk->icsk_rto = TCP_TIMEOUT_INIT;
 		newicsk->icsk_ack.lrcvtime = tcp_time_stamp;
+		newicsk->icsk_inet.mc_list = NULL;
 
 		newtp->packets_out = 0;
 		newtp->retrans_out = 0;