4.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jason Baron <jbaron@xxxxxxxxxx>
[ Upstream commit 083ae308280d13d187512b9babe3454342a7987e ]
The per-socket rate limit for 'challenge acks' was introduced in the
context of limiting ack loops:
commit f2b2c582e824 ("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: [PATCH 4.6 05/56] tcp: make challenge acks less predictable
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Neal Cardwell <ncardwell@xxxxxxxxxx>
Cc: Yuchung Cheng <ycheng@xxxxxxxxxx>
Cc: Yue Cao <ycao009@xxxxxxx>
Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_input.c | 39 ++++++++++++++++++++++-----------------
1 file changed, 22 insertions(+), 17 deletions(-)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3423,6 +3423,23 @@ static int tcp_ack_update_window(struct
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_BH(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
@@ -3436,21 +3453,9 @@ bool tcp_oow_rate_limited(struct net *ne
/* 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;
-
- if (*last_oow_ack_time) {
- s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
+ return false;
- if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
- NET_INC_STATS_BH(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] */
@@ -3463,9 +3468,9 @@ static void tcp_send_challenge_ack(struc
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. */
--
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