![Jason A. Donenfeld](/assets/img/avatar_default.png)
It turns out there's an easy way to get packets queued up while still having an MTU of zero, and that's via persistent keep alive. This commit makes sure that in whatever condition, we don't wind up dividing by zero. Note that an MTU of zero for a wireguard interface is something quasi-valid, so I don't think the correct fix is to limit it via min_mtu. This can be reproduced easily with: ip link add wg0 type wireguard ip link add wg1 type wireguard ip link set wg0 up mtu 0 ip link set wg1 up wg set wg0 private-key <(wg genkey) wg set wg1 listen-port 1 private-key <(wg genkey) peer $(wg show wg0 public-key) wg set wg0 peer $(wg show wg1 public-key) persistent-keepalive 1 endpoint 127.0.0.1:1 However, while min_mtu=0 seems fine, it makes sense to restrict the max_mtu. This commit also restricts the maximum MTU to the greatest number for which rounding up to the padding multiple won't overflow a signed integer. Packets this large were always rejected anyway eventually, due to checks deeper in, but it seems more sound not to even let the administrator configure something that won't work anyway. We use this opportunity to clean up this function a bit so that it's clear which paths we're expecting. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
420 lines
13 KiB
C
420 lines
13 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
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*/
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#include "queueing.h"
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#include "timers.h"
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#include "device.h"
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#include "peer.h"
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#include "socket.h"
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#include "messages.h"
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#include "cookie.h"
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#include <linux/uio.h>
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#include <linux/inetdevice.h>
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#include <linux/socket.h>
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#include <net/ip_tunnels.h>
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#include <net/udp.h>
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#include <net/sock.h>
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static void wg_packet_send_handshake_initiation(struct wg_peer *peer)
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{
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struct message_handshake_initiation packet;
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if (!wg_birthdate_has_expired(atomic64_read(&peer->last_sent_handshake),
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REKEY_TIMEOUT))
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return; /* This function is rate limited. */
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atomic64_set(&peer->last_sent_handshake, ktime_get_coarse_boottime_ns());
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net_dbg_ratelimited("%s: Sending handshake initiation to peer %llu (%pISpfsc)\n",
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peer->device->dev->name, peer->internal_id,
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&peer->endpoint.addr);
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if (wg_noise_handshake_create_initiation(&packet, &peer->handshake)) {
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wg_cookie_add_mac_to_packet(&packet, sizeof(packet), peer);
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wg_timers_any_authenticated_packet_traversal(peer);
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wg_timers_any_authenticated_packet_sent(peer);
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atomic64_set(&peer->last_sent_handshake,
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ktime_get_coarse_boottime_ns());
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wg_socket_send_buffer_to_peer(peer, &packet, sizeof(packet),
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HANDSHAKE_DSCP);
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wg_timers_handshake_initiated(peer);
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}
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}
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void wg_packet_handshake_send_worker(struct work_struct *work)
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{
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struct wg_peer *peer = container_of(work, struct wg_peer,
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transmit_handshake_work);
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wg_packet_send_handshake_initiation(peer);
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wg_peer_put(peer);
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}
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void wg_packet_send_queued_handshake_initiation(struct wg_peer *peer,
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bool is_retry)
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{
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if (!is_retry)
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peer->timer_handshake_attempts = 0;
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rcu_read_lock_bh();
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/* We check last_sent_handshake here in addition to the actual function
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* we're queueing up, so that we don't queue things if not strictly
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* necessary:
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*/
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if (!wg_birthdate_has_expired(atomic64_read(&peer->last_sent_handshake),
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REKEY_TIMEOUT) ||
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unlikely(READ_ONCE(peer->is_dead)))
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goto out;
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wg_peer_get(peer);
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/* Queues up calling packet_send_queued_handshakes(peer), where we do a
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* peer_put(peer) after:
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*/
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if (!queue_work(peer->device->handshake_send_wq,
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&peer->transmit_handshake_work))
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/* If the work was already queued, we want to drop the
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* extra reference:
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*/
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wg_peer_put(peer);
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out:
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rcu_read_unlock_bh();
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}
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void wg_packet_send_handshake_response(struct wg_peer *peer)
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{
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struct message_handshake_response packet;
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atomic64_set(&peer->last_sent_handshake, ktime_get_coarse_boottime_ns());
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net_dbg_ratelimited("%s: Sending handshake response to peer %llu (%pISpfsc)\n",
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peer->device->dev->name, peer->internal_id,
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&peer->endpoint.addr);
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if (wg_noise_handshake_create_response(&packet, &peer->handshake)) {
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wg_cookie_add_mac_to_packet(&packet, sizeof(packet), peer);
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if (wg_noise_handshake_begin_session(&peer->handshake,
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&peer->keypairs)) {
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wg_timers_session_derived(peer);
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wg_timers_any_authenticated_packet_traversal(peer);
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wg_timers_any_authenticated_packet_sent(peer);
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atomic64_set(&peer->last_sent_handshake,
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ktime_get_coarse_boottime_ns());
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wg_socket_send_buffer_to_peer(peer, &packet,
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sizeof(packet),
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HANDSHAKE_DSCP);
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}
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}
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}
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void wg_packet_send_handshake_cookie(struct wg_device *wg,
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struct sk_buff *initiating_skb,
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__le32 sender_index)
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{
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struct message_handshake_cookie packet;
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net_dbg_skb_ratelimited("%s: Sending cookie response for denied handshake message for %pISpfsc\n",
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wg->dev->name, initiating_skb);
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wg_cookie_message_create(&packet, initiating_skb, sender_index,
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&wg->cookie_checker);
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wg_socket_send_buffer_as_reply_to_skb(wg, initiating_skb, &packet,
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sizeof(packet));
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}
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static void keep_key_fresh(struct wg_peer *peer)
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{
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struct noise_keypair *keypair;
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bool send = false;
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rcu_read_lock_bh();
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keypair = rcu_dereference_bh(peer->keypairs.current_keypair);
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if (likely(keypair && READ_ONCE(keypair->sending.is_valid)) &&
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(unlikely(atomic64_read(&keypair->sending.counter.counter) >
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REKEY_AFTER_MESSAGES) ||
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(keypair->i_am_the_initiator &&
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unlikely(wg_birthdate_has_expired(keypair->sending.birthdate,
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REKEY_AFTER_TIME)))))
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send = true;
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rcu_read_unlock_bh();
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if (send)
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wg_packet_send_queued_handshake_initiation(peer, false);
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}
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static unsigned int calculate_skb_padding(struct sk_buff *skb)
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{
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unsigned int padded_size, last_unit = skb->len;
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if (unlikely(!PACKET_CB(skb)->mtu))
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return ALIGN(last_unit, MESSAGE_PADDING_MULTIPLE) - last_unit;
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/* We do this modulo business with the MTU, just in case the networking
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* layer gives us a packet that's bigger than the MTU. In that case, we
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* wouldn't want the final subtraction to overflow in the case of the
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* padded_size being clamped. Fortunately, that's very rarely the case,
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* so we optimize for that not happening.
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*/
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if (unlikely(last_unit > PACKET_CB(skb)->mtu))
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last_unit %= PACKET_CB(skb)->mtu;
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padded_size = min(PACKET_CB(skb)->mtu,
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ALIGN(last_unit, MESSAGE_PADDING_MULTIPLE));
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return padded_size - last_unit;
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}
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static bool encrypt_packet(struct sk_buff *skb, struct noise_keypair *keypair)
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{
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unsigned int padding_len, plaintext_len, trailer_len;
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struct scatterlist sg[MAX_SKB_FRAGS + 8];
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struct message_data *header;
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struct sk_buff *trailer;
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int num_frags;
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/* Calculate lengths. */
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padding_len = calculate_skb_padding(skb);
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trailer_len = padding_len + noise_encrypted_len(0);
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plaintext_len = skb->len + padding_len;
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/* Expand data section to have room for padding and auth tag. */
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num_frags = skb_cow_data(skb, trailer_len, &trailer);
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if (unlikely(num_frags < 0 || num_frags > ARRAY_SIZE(sg)))
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return false;
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/* Set the padding to zeros, and make sure it and the auth tag are part
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* of the skb.
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*/
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memset(skb_tail_pointer(trailer), 0, padding_len);
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/* Expand head section to have room for our header and the network
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* stack's headers.
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*/
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if (unlikely(skb_cow_head(skb, DATA_PACKET_HEAD_ROOM) < 0))
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return false;
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/* Finalize checksum calculation for the inner packet, if required. */
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if (unlikely(skb->ip_summed == CHECKSUM_PARTIAL &&
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skb_checksum_help(skb)))
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return false;
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/* Only after checksumming can we safely add on the padding at the end
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* and the header.
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*/
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skb_set_inner_network_header(skb, 0);
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header = (struct message_data *)skb_push(skb, sizeof(*header));
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header->header.type = cpu_to_le32(MESSAGE_DATA);
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header->key_idx = keypair->remote_index;
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header->counter = cpu_to_le64(PACKET_CB(skb)->nonce);
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pskb_put(skb, trailer, trailer_len);
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/* Now we can encrypt the scattergather segments */
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sg_init_table(sg, num_frags);
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if (skb_to_sgvec(skb, sg, sizeof(struct message_data),
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noise_encrypted_len(plaintext_len)) <= 0)
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return false;
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return chacha20poly1305_encrypt_sg_inplace(sg, plaintext_len, NULL, 0,
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PACKET_CB(skb)->nonce,
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keypair->sending.key);
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}
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void wg_packet_send_keepalive(struct wg_peer *peer)
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{
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struct sk_buff *skb;
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if (skb_queue_empty(&peer->staged_packet_queue)) {
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skb = alloc_skb(DATA_PACKET_HEAD_ROOM + MESSAGE_MINIMUM_LENGTH,
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GFP_ATOMIC);
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if (unlikely(!skb))
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return;
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skb_reserve(skb, DATA_PACKET_HEAD_ROOM);
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skb->dev = peer->device->dev;
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PACKET_CB(skb)->mtu = skb->dev->mtu;
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skb_queue_tail(&peer->staged_packet_queue, skb);
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net_dbg_ratelimited("%s: Sending keepalive packet to peer %llu (%pISpfsc)\n",
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peer->device->dev->name, peer->internal_id,
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&peer->endpoint.addr);
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}
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wg_packet_send_staged_packets(peer);
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}
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static void wg_packet_create_data_done(struct sk_buff *first,
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struct wg_peer *peer)
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{
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struct sk_buff *skb, *next;
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bool is_keepalive, data_sent = false;
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wg_timers_any_authenticated_packet_traversal(peer);
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wg_timers_any_authenticated_packet_sent(peer);
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skb_list_walk_safe(first, skb, next) {
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is_keepalive = skb->len == message_data_len(0);
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if (likely(!wg_socket_send_skb_to_peer(peer, skb,
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PACKET_CB(skb)->ds) && !is_keepalive))
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data_sent = true;
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}
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if (likely(data_sent))
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wg_timers_data_sent(peer);
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keep_key_fresh(peer);
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}
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void wg_packet_tx_worker(struct work_struct *work)
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{
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struct crypt_queue *queue = container_of(work, struct crypt_queue,
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work);
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struct noise_keypair *keypair;
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enum packet_state state;
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struct sk_buff *first;
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struct wg_peer *peer;
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while ((first = __ptr_ring_peek(&queue->ring)) != NULL &&
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(state = atomic_read_acquire(&PACKET_CB(first)->state)) !=
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PACKET_STATE_UNCRYPTED) {
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__ptr_ring_discard_one(&queue->ring);
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peer = PACKET_PEER(first);
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keypair = PACKET_CB(first)->keypair;
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if (likely(state == PACKET_STATE_CRYPTED))
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wg_packet_create_data_done(first, peer);
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else
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kfree_skb_list(first);
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wg_noise_keypair_put(keypair, false);
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wg_peer_put(peer);
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}
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}
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void wg_packet_encrypt_worker(struct work_struct *work)
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{
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struct crypt_queue *queue = container_of(work, struct multicore_worker,
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work)->ptr;
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struct sk_buff *first, *skb, *next;
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while ((first = ptr_ring_consume_bh(&queue->ring)) != NULL) {
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enum packet_state state = PACKET_STATE_CRYPTED;
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skb_list_walk_safe(first, skb, next) {
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if (likely(encrypt_packet(skb,
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PACKET_CB(first)->keypair))) {
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wg_reset_packet(skb);
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} else {
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state = PACKET_STATE_DEAD;
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break;
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}
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}
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wg_queue_enqueue_per_peer(&PACKET_PEER(first)->tx_queue, first,
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state);
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}
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}
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static void wg_packet_create_data(struct sk_buff *first)
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{
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struct wg_peer *peer = PACKET_PEER(first);
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struct wg_device *wg = peer->device;
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int ret = -EINVAL;
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rcu_read_lock_bh();
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if (unlikely(READ_ONCE(peer->is_dead)))
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goto err;
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ret = wg_queue_enqueue_per_device_and_peer(&wg->encrypt_queue,
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&peer->tx_queue, first,
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wg->packet_crypt_wq,
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&wg->encrypt_queue.last_cpu);
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if (unlikely(ret == -EPIPE))
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wg_queue_enqueue_per_peer(&peer->tx_queue, first,
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PACKET_STATE_DEAD);
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err:
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rcu_read_unlock_bh();
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if (likely(!ret || ret == -EPIPE))
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return;
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wg_noise_keypair_put(PACKET_CB(first)->keypair, false);
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wg_peer_put(peer);
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kfree_skb_list(first);
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}
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void wg_packet_purge_staged_packets(struct wg_peer *peer)
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{
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spin_lock_bh(&peer->staged_packet_queue.lock);
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peer->device->dev->stats.tx_dropped += peer->staged_packet_queue.qlen;
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__skb_queue_purge(&peer->staged_packet_queue);
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spin_unlock_bh(&peer->staged_packet_queue.lock);
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}
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void wg_packet_send_staged_packets(struct wg_peer *peer)
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{
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struct noise_symmetric_key *key;
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struct noise_keypair *keypair;
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struct sk_buff_head packets;
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struct sk_buff *skb;
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/* Steal the current queue into our local one. */
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__skb_queue_head_init(&packets);
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spin_lock_bh(&peer->staged_packet_queue.lock);
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skb_queue_splice_init(&peer->staged_packet_queue, &packets);
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spin_unlock_bh(&peer->staged_packet_queue.lock);
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if (unlikely(skb_queue_empty(&packets)))
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return;
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/* First we make sure we have a valid reference to a valid key. */
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rcu_read_lock_bh();
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keypair = wg_noise_keypair_get(
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rcu_dereference_bh(peer->keypairs.current_keypair));
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rcu_read_unlock_bh();
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if (unlikely(!keypair))
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goto out_nokey;
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key = &keypair->sending;
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if (unlikely(!READ_ONCE(key->is_valid)))
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goto out_nokey;
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if (unlikely(wg_birthdate_has_expired(key->birthdate,
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REJECT_AFTER_TIME)))
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goto out_invalid;
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/* After we know we have a somewhat valid key, we now try to assign
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* nonces to all of the packets in the queue. If we can't assign nonces
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* for all of them, we just consider it a failure and wait for the next
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* handshake.
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*/
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skb_queue_walk(&packets, skb) {
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/* 0 for no outer TOS: no leak. TODO: at some later point, we
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* might consider using flowi->tos as outer instead.
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*/
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PACKET_CB(skb)->ds = ip_tunnel_ecn_encap(0, ip_hdr(skb), skb);
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PACKET_CB(skb)->nonce =
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atomic64_inc_return(&key->counter.counter) - 1;
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if (unlikely(PACKET_CB(skb)->nonce >= REJECT_AFTER_MESSAGES))
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goto out_invalid;
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}
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packets.prev->next = NULL;
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wg_peer_get(keypair->entry.peer);
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PACKET_CB(packets.next)->keypair = keypair;
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wg_packet_create_data(packets.next);
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return;
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out_invalid:
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WRITE_ONCE(key->is_valid, false);
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out_nokey:
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wg_noise_keypair_put(keypair, false);
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/* We orphan the packets if we're waiting on a handshake, so that they
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* don't block a socket's pool.
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*/
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skb_queue_walk(&packets, skb)
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skb_orphan(skb);
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/* Then we put them back on the top of the queue. We're not too
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* concerned about accidentally getting things a little out of order if
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* packets are being added really fast, because this queue is for before
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* packets can even be sent and it's small anyway.
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*/
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spin_lock_bh(&peer->staged_packet_queue.lock);
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skb_queue_splice(&packets, &peer->staged_packet_queue);
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spin_unlock_bh(&peer->staged_packet_queue.lock);
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/* If we're exiting because there's something wrong with the key, it
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* means we should initiate a new handshake.
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*/
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wg_packet_send_queued_handshake_initiation(peer, false);
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}
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