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tcp: allow to turn tcp timestamp randomization off 

Eric says: "By looking at tcpdump, and TS val of xmit packets of multiple
flows, we can deduct the relative qdisc delays (think of fq pacing).
This should work even if we have one flow per remote peer."

Having random per flow (or host) offsets doesn't allow that anymore so add
a way to turn this off.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-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:
Florian Westphal 2016-12-01 11:32:07 +01:00 committed by David S. Miller
parent 95a22caee3
commit 25429d7b7d
3 changed files with 11 additions and 4 deletions
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9
Documentation/networking/ip-sysctl.txt
View File

@ -610,8 +610,13 @@ tcp_syn_retries - INTEGER
with the current initial RTO of 1second. With this the final timeout
for an active TCP connection attempt will happen after 127seconds.
tcp_timestamps - BOOLEAN
Enable timestamps as defined in RFC1323.
tcp_timestamps - INTEGER
Enable timestamps as defined in RFC1323.
0: Disabled.
1: Enable timestamps as defined in RFC1323 and use random offset for
each connection rather than only using the current time.
2: Like 1, but without random offsets.
Default: 1
tcp_min_tso_segs - INTEGER
Minimal number of segments per TSO frame.

5
net/core/secure_seq.c
View File

@ -12,6 +12,7 @@
#include <net/secure_seq.h>
#if IS_ENABLED(CONFIG_IPV6) || IS_ENABLED(CONFIG_INET)
#include <net/tcp.h>
#define NET_SECRET_SIZE (MD5_MESSAGE_BYTES / 4)
static u32 net_secret[NET_SECRET_SIZE] ____cacheline_aligned;
@ -58,7 +59,7 @@ u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
md5_transform(hash, secret);
*tsoff = hash[1];
*tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
return seq_scale(hash[0]);
}
EXPORT_SYMBOL(secure_tcpv6_sequence_number);
@ -100,7 +101,7 @@ u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
md5_transform(hash, net_secret);
*tsoff = hash[1];
*tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
return seq_scale(hash[0]);
}

1
net/ipv4/tcp_input.c
View File

@ -85,6 +85,7 @@ int sysctl_tcp_dsack __read_mostly = 1;
int sysctl_tcp_app_win __read_mostly = 31;
int sysctl_tcp_adv_win_scale __read_mostly = 1;
EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
EXPORT_SYMBOL(sysctl_tcp_timestamps);
/* rfc5961 challenge ack rate limiting */
int sysctl_tcp_challenge_ack_limit = 1000;