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Commit 264ea103 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarFlorian Westphal <fw@strlen.de>
Acked-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c24a5964

include/net/tcp.h

+24 −14
Original line number Diff line number Diff line
@@ -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;
@@ -484,12 +472,34 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb); 
 * the counter advances immediately after a cookie is generated).

 */

#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;

}