Messages in this thread | | | Date | Thu, 24 Sep 2015 07:49:08 -0700 | Subject | Re: [PATCH] tcp: Use absolute system clock for TCP timestamps | From | Eric Dumazet <> |
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On Thu, Sep 24, 2015 at 7:14 AM, Jovi Zhangwei <jovi@cloudflare.com> wrote: > From f455dc3958593250909627474100f6cc5c158a5c Mon Sep 17 00:00:00 2001 > From: Marek Majkowski <marek@cloudflare.com> > Date: Fri, 11 Sep 2015 06:05:07 -0700 > Subject: [PATCH] tcp: Use absolute system clock for TCP timestamps > > Using TCP timestamps is beneficial due for to its purpose in PAWS and when > its role when SYN cookies are enabled. In practice though TCP timestamps are > often disabled due to being a perceived security issue - they leak Linux > system uptime. > > This patch introduces a kernel option that makes TCP timestamp always return > an absolute value derived from a system clock as opposed to jiffies from > boot. > > This patch is based on the approach taken by grsecurity: > https://grsecurity.net/~spender/random_timestamp.diff >
Please do not send html messages, they wont reach lists.
May I ask how this patch was really tested ?
It cannot possibly work on current kernels, as TCP Timestamps are generated from clock samples taken from skb_mstamp_get(), and you did not change it.
static inline void skb_mstamp_get(struct skb_mstamp *cl) { u64 val = local_clock();
do_div(val, NSEC_PER_USEC); cl->stamp_us = (u32)val; cl->stamp_jiffies = (u32)jiffies; }
TCP stack uses tcp_time_stamp internally, we do not want to add overhead adding an offset on all places.
tp->lsndtime is an example, but we have others.
Therefore, I suggest you add a new function and use it only where needed.
static inline u32 secure_tcp_time_stamp(void) { returns (u32)(tcp_time_stamp + rtc_timestamp_base); }
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