dccp/tcp: do not inherit mc_list from parent

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 <[email protected]>
Reported-by: Pray3r <[email protected]>
Reported-by: Andrey Konovalov <[email protected]>
Tested-by: Andrey Konovalov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 5e313c1ac94fc88eca5fe3a0e9e46e551e955ff0..1054d330bf9df3189a21dbb08e27c0e6ad136775 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -794,6 +794,8 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
                /* listeners have SOCK_RCU_FREE, not the children */
                sock_reset_flag(newsk, SOCK_RCU_FREE);
 
+               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));