Commit 7db92362 authored Mar 01, 2017 by Wei Wang Committed by David S. Miller Mar 02, 2017

tcp: fix potential double free issue for fastopen_req



tp->fastopen_req could potentially be double freed if a malicious
user does the following:
1. Enable TCP_FASTOPEN_CONNECT sockopt and do a connect() on the socket.
2. Call connect() with AF_UNSPEC to disconnect the socket.
3. Make this socket a listening socket by calling listen().
4. Accept incoming connections and generate child sockets. All child
   sockets will get a copy of the pointer of fastopen_req.
5. Call close() on all sockets. fastopen_req will get freed multiple
   times.

Fixes: 19f6d3f3 ("net/tcp-fastopen: Add new API support")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 94352d45

net/ipv4/tcp.c

+12 −3

Original line number	Diff line number	Diff line
		@@ -1110,9 +1110,14 @@ static int tcp_sendmsg_fastopen(struct sock sk, struct msghdr msg,
		flags = (msg->msg_flags & MSG_DONTWAIT) ? O_NONBLOCK : 0;
		err = __inet_stream_connect(sk->sk_socket, msg->msg_name,
		msg->msg_namelen, flags, 1);
		inet->defer_connect = 0;
		/* fastopen_req could already be freed in __inet_stream_connect
		* if the connection times out or gets rst
		*/
		if (tp->fastopen_req) {
		*copied = tp->fastopen_req->copied;
		tcp_free_fastopen_req(tp);
		inet->defer_connect = 0;
		}
		return err;
		}

		@@ -2318,6 +2323,10 @@ int tcp_disconnect(struct sock *sk, int flags)
		memset(&tp->rx_opt, 0, sizeof(tp->rx_opt));
		__sk_dst_reset(sk);

		/* Clean up fastopen related fields */
		tcp_free_fastopen_req(tp);
		inet->defer_connect = 0;

		WARN_ON(inet->inet_num && !icsk->icsk_bind_hash);

		sk->sk_error_report(sk);

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