tcp: syncookies: do not use getnstimeofday() (63262315) · Commits · 戴 / test

While it is true that getnstimeofday() uses about 40 cycles if TSC is available, it can use 1600 cycles if hpet is the clocksource. Switch to get_jiffies_64(), as this is more than enough, and go back to 60 seconds periods. Fixes: ("tcp: syncookies: reduce cookie lifetime to 128 seconds") Signed-off-by:

Eric Dumazet <edumazet@google.com> Cc: Florian Westphal <fw@strlen.de> Acked-by:

Florian Westphal <fw@strlen.de> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/net/tcp.h

+6 −5

Original line number	Diff line number	Diff line
		@@ -480,20 +480,21 @@ struct sock cookie_v4_check(struct sock sk, struct sk_buff *skb,
		#ifdef CONFIG_SYN_COOKIES
		#include <linux/ktime.h>

		/* Syncookies use a monotonic timer which increments every 64 seconds.
		/* Syncookies use a monotonic timer which increments every 60 seconds.
		* This counter is used both as a hash input and partially encoded into
		* the cookie value. A cookie is only validated further if the delta
		* between the current counter value and the encoded one is less than this,
		* i.e. a sent cookie is valid only at most for 128 seconds (or less if
		* 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

		static inline u32 tcp_cookie_time(void)
		{
		struct timespec now;
		getnstimeofday(&now);
		return now.tv_sec >> 6; /* 64 seconds granularity */
		u64 val = get_jiffies_64();

		do_div(val, 60 * HZ);
		return val;
		}

		u32 __cookie_v4_init_sequence(const struct iphdr iph, const struct tcphdr th,

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