Randomized TCP client ports

Randomized TCP client ports

[Walter Huf]

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In the course of developing netboot menus, and rebooting my virtual machine
often, I am running into a problem where Grub is reusing the same TCP
client ports across reboots, and my server (because of TCP TIME_WAIT)
objects to this.

I have a small change to set the initial client port based on
grub_rtc_get_time_ms(), but I'm not sure if that functionality is available
on all supported platforms. I'd like to provide a general contribution that
works on all platforms.

Is there a general way to get a pseudo-random integer that is different on
each boot?

Thank you very much!

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Re: Randomized TCP client ports

[Daniel Kiper]

Hi Walter,

On Wed, Nov 23, 2016 at 01:04:20PM -0800, Walter Huf wrote:
> In the course of developing netboot menus, and rebooting my virtual machine
> often, I am running into a problem where Grub is reusing the same TCP
> client ports across reboots, and my server (because of TCP TIME_WAIT)
> objects to this.
>
> I have a small change to set the initial client port based on
> grub_rtc_get_time_ms(), but I'm not sure if that functionality is available
> on all supported platforms. I'd like to provide a general contribution that
> works on all platforms.
>
> Is there a general way to get a pseudo-random integer that is different on
> each boot?

I think that you should take a look, at least, at random module,
grub-core/lib/random.c, etc.

Have a nice weekend,

Daniel

Re: Randomized TCP client ports

[Andrei Borzenkov]

26.11.2016 00:47, Daniel Kiper пишет:
> Hi Walter,
> 
> On Wed, Nov 23, 2016 at 01:04:20PM -0800, Walter Huf wrote:
>> In the course of developing netboot menus, and rebooting my virtual machine
>> often, I am running into a problem where Grub is reusing the same TCP
>> client ports across reboots, and my server (because of TCP TIME_WAIT)
>> objects to this.
>>
>> I have a small change to set the initial client port based on
>> grub_rtc_get_time_ms(), but I'm not sure if that functionality is available
>> on all supported platforms. I'd like to provide a general contribution that
>> works on all platforms.
>>

This function is not universally available; it is used as implementation
of grub_get_time_ms() which you probably should use instead, as it is
guaranteed to exist.

>> Is there a general way to get a pseudo-random integer that is different on
>> each boot?
> 
> I think that you should take a look, at least, at random module,
> grub-core/lib/random.c, etc.
> 

It relies on platform providing random value and so far it works for x86
with tsc and pmtimer only.