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tcp: syncookies: extend validity range

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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 <edumazet@google.com>
Acked-by: Florian Westphal <fw@strlen.de>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-05-14 14:26:56 -07:00 committed by David S. Miller
parent c24a59649f
commit 264ea103a7
1 changed files with 24 additions and 14 deletions
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38
include/net/tcp.h
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@ -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;
}