From 264ea103a7473f51aced838e68ed384ea2c759f5 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 14 May 2015 14:26:56 -0700 Subject: [PATCH] tcp: syncookies: extend validity range Now we allow storing more request socks per listener, we might hit syncookie mode less often and hit following bug in our stack : When we send a burst of syncookies, then exit this mode, tcp_synq_no_recent_overflow() can return false if the ACK packets coming from clients are coming three seconds after the end of syncookie episode. This is a way too strong requirement and conflicts with rest of syncookie code which allows ACK to be aged up to 2 minutes. Perfectly valid ACK packets are dropped just because clients might be in a crowded wifi environment or on another planet. So let's fix this, and also change tcp_synq_overflow() to not dirty a cache line for every syncookie we send, as we are under attack. Signed-off-by: Eric Dumazet Acked-by: Florian Westphal Acked-by: Yuchung Cheng Signed-off-by: David S. Miller --- include/net/tcp.h | 38 ++++++++++++++++++++++++-------------- 1 file changed, 24 insertions(+), 14 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index b8ea12880fd9..7ace6acbf5fd 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -326,18 +326,6 @@ static inline bool tcp_too_many_orphans(struct sock *sk, int shift) bool tcp_check_oom(struct sock *sk, int shift); -/* syncookies: remember time of last synqueue overflow */ -static inline void tcp_synq_overflow(struct sock *sk) -{ - tcp_sk(sk)->rx_opt.ts_recent_stamp = jiffies; -} - -/* syncookies: no recent synqueue overflow on this listening socket? */ -static inline bool tcp_synq_no_recent_overflow(const struct sock *sk) -{ - unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp; - return time_after(jiffies, last_overflow + TCP_TIMEOUT_FALLBACK); -} extern struct proto tcp_prot; @@ -483,13 +471,35 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb); * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if * the counter advances immediately after a cookie is generated). */ -#define MAX_SYNCOOKIE_AGE 2 +#define MAX_SYNCOOKIE_AGE 2 +#define TCP_SYNCOOKIE_PERIOD (60 * HZ) +#define TCP_SYNCOOKIE_VALID (MAX_SYNCOOKIE_AGE * TCP_SYNCOOKIE_PERIOD) + +/* syncookies: remember time of last synqueue overflow + * But do not dirty this field too often (once per second is enough) + */ +static inline void tcp_synq_overflow(struct sock *sk) +{ + unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp; + unsigned long now = jiffies; + + if (time_after(now, last_overflow + HZ)) + tcp_sk(sk)->rx_opt.ts_recent_stamp = now; +} + +/* syncookies: no recent synqueue overflow on this listening socket? */ +static inline bool tcp_synq_no_recent_overflow(const struct sock *sk) +{ + unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp; + + return time_after(jiffies, last_overflow + TCP_SYNCOOKIE_VALID); +} static inline u32 tcp_cookie_time(void) { u64 val = get_jiffies_64(); - do_div(val, 60 * HZ); + do_div(val, TCP_SYNCOOKIE_PERIOD); return val; } -- 2.20.1