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tcp: enable per-socket rate limiting of all 'challenge acks' 

The per-socket rate limit for 'challenge acks' was introduced in the
context of limiting ack loops:

commit f2b2c582e8 ("tcp: mitigate ACK loops for connections as tcp_sock")

And I think it can be extended to rate limit all 'challenge acks' on a
per-socket basis.

Since we have the global tcp_challenge_ack_limit, this patch allows for
tcp_challenge_ack_limit to be set to a large value and effectively rely on
the per-socket limit, or set tcp_challenge_ack_limit to a lower value and
still prevents a single connections from consuming the entire challenge ack
quota.

It further moves in the direction of eliminating the global limit at some
point, as Eric Dumazet has suggested. This a follow-up to:
Subject: tcp: make challenge acks less predictable

Cc: Eric Dumazet <edumazet@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Yue Cao <ycao009@ucr.edu>
Signed-off-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Baron 2016-07-14 11:38:40 -04:00 committed by David S. Miller
parent 005db31d5f
commit 083ae30828
1 changed files with 22 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
net/ipv4/tcp_input.c
View File

@ -3421,6 +3421,23 @@ static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32
return flag;
}
static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
u32 *last_oow_ack_time)
{
if (*last_oow_ack_time) {
s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
NET_INC_STATS(net, mib_idx);
return true; /* rate-limited: don't send yet! */
}
}
*last_oow_ack_time = tcp_time_stamp;
return false; /* not rate-limited: go ahead, send dupack now! */
}
/* Return true if we're currently rate-limiting out-of-window ACKs and
* thus shouldn't send a dupack right now. We rate-limit dupacks in
* response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
@ -3434,21 +3451,9 @@ bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
/* Data packets without SYNs are not likely part of an ACK loop. */
if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
!tcp_hdr(skb)->syn)
goto not_rate_limited;
return false;
if (*last_oow_ack_time) {
s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
NET_INC_STATS(net, mib_idx);
return true; /* rate-limited: don't send yet! */
}
}
*last_oow_ack_time = tcp_time_stamp;
not_rate_limited:
return false; /* not rate-limited: go ahead, send dupack now! */
return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
}
/* RFC 5961 7 [ACK Throttling] */
@ -3461,9 +3466,9 @@ static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
u32 count, now;
/* First check our per-socket dupack rate limit. */
if (tcp_oow_rate_limited(sock_net(sk), skb,
LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
&tp->last_oow_ack_time))
if (__tcp_oow_rate_limited(sock_net(sk),
LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
&tp->last_oow_ack_time))
return;
/* Then check host-wide RFC 5961 rate limit. */