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https://github.com/openwrt/openwrt.git
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96 lines
3.9 KiB
Diff
96 lines
3.9 KiB
Diff
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
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Date: Fri, 14 Feb 2020 23:57:22 +0100
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Subject: [PATCH] wireguard: send: account for mtu=0 devices
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commit 175f1ca9a9ed8689d2028da1a7c624bb4fb4ff7e upstream.
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It turns out there's an easy way to get packets queued up while still
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having an MTU of zero, and that's via persistent keep alive. This commit
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makes sure that in whatever condition, we don't wind up dividing by
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zero. Note that an MTU of zero for a wireguard interface is something
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quasi-valid, so I don't think the correct fix is to limit it via
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min_mtu. This can be reproduced easily with:
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ip link add wg0 type wireguard
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ip link add wg1 type wireguard
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ip link set wg0 up mtu 0
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ip link set wg1 up
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wg set wg0 private-key <(wg genkey)
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wg set wg1 listen-port 1 private-key <(wg genkey) peer $(wg show wg0 public-key)
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wg set wg0 peer $(wg show wg1 public-key) persistent-keepalive 1 endpoint 127.0.0.1:1
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However, while min_mtu=0 seems fine, it makes sense to restrict the
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max_mtu. This commit also restricts the maximum MTU to the greatest
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number for which rounding up to the padding multiple won't overflow a
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signed integer. Packets this large were always rejected anyway
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eventually, due to checks deeper in, but it seems more sound not to even
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let the administrator configure something that won't work anyway.
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We use this opportunity to clean up this function a bit so that it's
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clear which paths we're expecting.
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Cc: Eric Dumazet <eric.dumazet@gmail.com>
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Reviewed-by: Eric Dumazet <edumazet@google.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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---
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drivers/net/wireguard/device.c | 7 ++++---
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drivers/net/wireguard/send.c | 16 +++++++++++-----
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2 files changed, 15 insertions(+), 8 deletions(-)
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--- a/drivers/net/wireguard/device.c
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+++ b/drivers/net/wireguard/device.c
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@@ -258,6 +258,8 @@ static void wg_setup(struct net_device *
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enum { WG_NETDEV_FEATURES = NETIF_F_HW_CSUM | NETIF_F_RXCSUM |
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NETIF_F_SG | NETIF_F_GSO |
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NETIF_F_GSO_SOFTWARE | NETIF_F_HIGHDMA };
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+ const int overhead = MESSAGE_MINIMUM_LENGTH + sizeof(struct udphdr) +
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+ max(sizeof(struct ipv6hdr), sizeof(struct iphdr));
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dev->netdev_ops = &netdev_ops;
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dev->hard_header_len = 0;
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@@ -271,9 +273,8 @@ static void wg_setup(struct net_device *
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dev->features |= WG_NETDEV_FEATURES;
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dev->hw_features |= WG_NETDEV_FEATURES;
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dev->hw_enc_features |= WG_NETDEV_FEATURES;
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- dev->mtu = ETH_DATA_LEN - MESSAGE_MINIMUM_LENGTH -
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- sizeof(struct udphdr) -
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- max(sizeof(struct ipv6hdr), sizeof(struct iphdr));
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+ dev->mtu = ETH_DATA_LEN - overhead;
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+ dev->max_mtu = round_down(INT_MAX, MESSAGE_PADDING_MULTIPLE) - overhead;
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SET_NETDEV_DEVTYPE(dev, &device_type);
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--- a/drivers/net/wireguard/send.c
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+++ b/drivers/net/wireguard/send.c
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@@ -143,16 +143,22 @@ static void keep_key_fresh(struct wg_pee
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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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+
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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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+
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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.
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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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- unsigned int last_unit = skb->len % PACKET_CB(skb)->mtu;
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- unsigned int padded_size = ALIGN(last_unit, MESSAGE_PADDING_MULTIPLE);
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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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- if (padded_size > PACKET_CB(skb)->mtu)
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- padded_size = 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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