[PATCH Trusty] dccp/tcp: do not inherit mc_list from parent

[Stefan Bader]

From: Eric Dumazet <edumazet at google.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 at google.com>
Reported-by: Pray3r <pray3r.z at gmail.com>
Reported-by: Andrey Konovalov <andreyknvl at google.com>
Tested-by: Andrey Konovalov <andreyknvl at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>

CVE-2017-8890

(backported from 657831ffc38e30092a2d5f03d385d710eb88b09a)
[manually selected new context to apply]
Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
---
 net/ipv4/inet_connection_sock.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index fc0e649..92316d2 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -678,6 +678,7 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
 		inet_sk(newsk)->inet_dport = inet_rsk(req)->ir_rmt_port;
 		inet_sk(newsk)->inet_num = inet_rsk(req)->ir_num;
 		inet_sk(newsk)->inet_sport = htons(inet_rsk(req)->ir_num);
+		inet_sk(newsk)->mc_list = NULL;
 		newsk->sk_write_space = sk_stream_write_space;
 
 		newicsk->icsk_retransmits = 0;
-- 
2.7.4