From: Jason A. Donenfeld Date: Wed, 20 May 2020 04:49:29 +0000 (-0600) Subject: wireguard: queueing: preserve flow hash across packet scrubbing X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=c78a0b4a78839d572d8a80f6a62221c0d7843135;p=linux.git wireguard: queueing: preserve flow hash across packet scrubbing It's important that we clear most header fields during encapsulation and decapsulation, because the packet is substantially changed, and we don't want any info leak or logic bug due to an accidental correlation. But, for encapsulation, it's wrong to clear skb->hash, since it's used by fq_codel and flow dissection in general. Without it, classification does not proceed as usual. This change might make it easier to estimate the number of innerflows by examining clustering of out of order packets, but this shouldn't open up anything that can't already be inferred otherwise (e.g. syn packet size inference), and fq_codel can be disabled anyway. Furthermore, it might be the case that the hash isn't used or queried at all until after wireguard transmits the encrypted UDP packet, which means skb->hash might still be zero at this point, and thus no hash taken over the inner packet data. In order to address this situation, we force a calculation of skb->hash before encrypting packet data. Of course this means that fq_codel might transmit packets slightly more out of order than usual. Toke did some testing on beefy machines with high quantities of parallel flows and found that increasing the reply-attack counter to 8192 takes care of the most pathological cases pretty well. Reported-by: Dave Taht Reviewed-and-tested-by: Toke Høiland-Jørgensen Fixes: e7096c131e51 ("net: WireGuard secure network tunnel") Signed-off-by: Jason A. Donenfeld Signed-off-by: David S. Miller --- diff --git a/drivers/net/wireguard/messages.h b/drivers/net/wireguard/messages.h index b8a7b9ce32ba7..208da72673fc0 100644 --- a/drivers/net/wireguard/messages.h +++ b/drivers/net/wireguard/messages.h @@ -32,7 +32,7 @@ enum cookie_values { }; enum counter_values { - COUNTER_BITS_TOTAL = 2048, + COUNTER_BITS_TOTAL = 8192, COUNTER_REDUNDANT_BITS = BITS_PER_LONG, COUNTER_WINDOW_SIZE = COUNTER_BITS_TOTAL - COUNTER_REDUNDANT_BITS }; diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h index 3432232afe061..c58df439dbbe0 100644 --- a/drivers/net/wireguard/queueing.h +++ b/drivers/net/wireguard/queueing.h @@ -87,12 +87,20 @@ static inline bool wg_check_packet_protocol(struct sk_buff *skb) return real_protocol && skb->protocol == real_protocol; } -static inline void wg_reset_packet(struct sk_buff *skb) +static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating) { + u8 l4_hash = skb->l4_hash; + u8 sw_hash = skb->sw_hash; + u32 hash = skb->hash; skb_scrub_packet(skb, true); memset(&skb->headers_start, 0, offsetof(struct sk_buff, headers_end) - offsetof(struct sk_buff, headers_start)); + if (encapsulating) { + skb->l4_hash = l4_hash; + skb->sw_hash = sw_hash; + skb->hash = hash; + } skb->queue_mapping = 0; skb->nohdr = 0; skb->peeked = 0; diff --git a/drivers/net/wireguard/receive.c b/drivers/net/wireguard/receive.c index 3bb5b9ae7cd15..d0eebd90c9d50 100644 --- a/drivers/net/wireguard/receive.c +++ b/drivers/net/wireguard/receive.c @@ -484,7 +484,7 @@ int wg_packet_rx_poll(struct napi_struct *napi, int budget) if (unlikely(wg_socket_endpoint_from_skb(&endpoint, skb))) goto next; - wg_reset_packet(skb); + wg_reset_packet(skb, false); wg_packet_consume_data_done(peer, skb, &endpoint); free = false; diff --git a/drivers/net/wireguard/send.c b/drivers/net/wireguard/send.c index 6687db6998035..2f5119ff93d8f 100644 --- a/drivers/net/wireguard/send.c +++ b/drivers/net/wireguard/send.c @@ -167,6 +167,11 @@ static bool encrypt_packet(struct sk_buff *skb, struct noise_keypair *keypair) struct sk_buff *trailer; int num_frags; + /* Force hash calculation before encryption so that flow analysis is + * consistent over the inner packet. + */ + skb_get_hash(skb); + /* Calculate lengths. */ padding_len = calculate_skb_padding(skb); trailer_len = padding_len + noise_encrypted_len(0); @@ -295,7 +300,7 @@ void wg_packet_encrypt_worker(struct work_struct *work) skb_list_walk_safe(first, skb, next) { if (likely(encrypt_packet(skb, PACKET_CB(first)->keypair))) { - wg_reset_packet(skb); + wg_reset_packet(skb, true); } else { state = PACKET_STATE_DEAD; break;