linux-kernel - [PATCH 3.10 249/250] dccp/tcp: do not inherit mc

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Date:   Thu,  8 Jun 2017 01:00:35 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 249/250] dccp/tcp: do not inherit mc_list from parent

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

commit 657831ffc38e30092a2d5f03d385d710eb88b09a upstream.

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Willy Tarreau <w@....eu>
---
 net/ipv4/inet_connection_sock.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 6acb541..40ac1e2 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -688,6 +688,8 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
 		inet_sk(newsk)->inet_sport = inet_rsk(req)->loc_port;
 		newsk->sk_write_space = sk_stream_write_space;
 
+		inet_sk(newsk)->mc_list = NULL;
+
 		newicsk->icsk_retransmits = 0;
 		newicsk->icsk_backoff	  = 0;
 		newicsk->icsk_probes_out  = 0;
-- 
2.8.0.rc2.1.gbe9624a