Code: struct sock *inet_csk_clone_lock(const struct sock *sk,
				 const struct request_sock *req,
				 const gfp_t priority)
{
	struct sock *newsk = sk_clone_lock(sk, priority);

	if (newsk) {
		struct inet_connection_sock *newicsk = inet_csk(newsk);

		newsk->sk_state = TCP_SYN_RECV;
		newicsk->icsk_bind_hash = NULL;

		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);
		newsk->sk_write_space = sk_stream_write_space;

 		/* listeners have SOCK_RCU_FREE, not the children */
 		sock_reset_flag(newsk, SOCK_RCU_FREE);
 
 		newsk->sk_mark = inet_rsk(req)->ir_mark;
 		atomic64_set(&newsk->sk_cookie,
 			     atomic64_read(&inet_rsk(req)->ir_cookie));

		newicsk->icsk_retransmits = 0;
		newicsk->icsk_backoff	  = 0;
		newicsk->icsk_probes_out  = 0;

		/* Deinitialize accept_queue to trap illegal accesses. */
		memset(&newicsk->icsk_accept_queue, 0, sizeof(newicsk->icsk_accept_queue));

		security_inet_csk_clone(newsk, req);
	}
	return newsk;
}

Vulnerability Type: DoS 
CWE ID: CWE-415
Summary: The inet_csk_clone_lock function in net/ipv4/inet_connection_sock.c in the Linux kernel through 4.10.15 allows attackers to cause a denial of service (double free) or possibly have unspecified other impact by leveraging use of the accept system call.
Commit Message: 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 <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>