dccp/tcp: do not inherit mc_list from parent

[ Upstream commit 657831ffc38e30092a2d5f03d385d710eb88b09a ]

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@google.com>
Reported-by: Pray3r <pray3r.z@gmail.com>
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 64148914803a8443ecc0de2a45c141ae72cc0258..45fa2aaa3d3fe1c89609c47ea4315c954a68de6e 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -669,6 +669,8 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
                inet_sk(newsk)->inet_sport = htons(inet_rsk(req)->ir_num);
                newsk->sk_write_space = sk_stream_write_space;
 
+               inet_sk(newsk)->mc_list = NULL;
+
                newsk->sk_mark = inet_rsk(req)->ir_mark;
                atomic64_set(&newsk->sk_cookie,
                             atomic64_read(&inet_rsk(req)->ir_cookie));