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Date: Mon, 07 Jan 2013 10:48:52 -0500
From: Vlad Yasevich <vyasevich@...il.com>
To: Neil Horman <nhorman@...driver.com>
CC: Florian Fainelli <florian@...nwrt.org>, netdev@...r.kernel.org,
David Miller <davem@...emloft.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-sctp@...r.kernel.org
Subject: Re: [PATCH v2] sctp: Change defaults on cookie hmac selection
On 01/07/2013 10:38 AM, Neil Horman wrote:
> On Mon, Jan 07, 2013 at 04:15:24PM +0100, Florian Fainelli wrote:
>> Le 01/07/13 15:49, Neil Horman a écrit :
>>> On Mon, Jan 07, 2013 at 02:25:39PM +0100, Florian Fainelli wrote:
>>>> Hello Neil,
>>>>
>>>> Le 12/15/12 02:22, Neil Horman a écrit :
>>>>> Recently I posted commit 3c68198e75 which made selection of the cookie hmac
>>>>> algorithm selectable. This is all well and good, but Linus noted that it
>>>>> changes the default config:
>>>>> http://marc.info/?l=linux-netdev&m=135536629004808&w=2
>>>>>
>>>>> I've modified the sctp Kconfig file to reflect the recommended way of making
>>>>> this choice, using the thermal driver example specified, and brought the
>>>>> defaults back into line with the way they were prior to my origional patch
>>>>>
>>>>> Also, on Linus' suggestion, re-adding ability to select default 'none' hmac
>>>>> algorithm, so we don't needlessly bloat the kernel by forcing a non-none
>>>>> default. This also led me to note that we won't honor the default none
>>>>> condition properly because of how sctp_net_init is encoded. Fix that up as
>>>>> well.
>>>>>
>>>>> Tested by myself (allbeit fairly quickly). All configuration combinations seems
>>>>> to work soundly.
>>>>>
>>>>> Signed-off-by: Neil Horman <nhorman@...driver.com>
>>>>> CC: David Miller <davem@...emloft.net>
>>>>> CC: Linus Torvalds <torvalds@...ux-foundation.org>
>>>>> CC: Vlad Yasevich <vyasevich@...il.com>
>>>>> CC: linux-sctp@...r.kernel.org
>>>>> ---
>>>>> net/sctp/Kconfig | 27 +++++++++++++++++++++++++--
>>>>> net/sctp/protocol.c | 4 ++--
>>>>> 2 files changed, 27 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/net/sctp/Kconfig b/net/sctp/Kconfig
>>>>> index a9edd2e..c262106 100644
>>>>> --- a/net/sctp/Kconfig
>>>>> +++ b/net/sctp/Kconfig
>>>>> @@ -66,12 +66,36 @@ config SCTP_DBG_OBJCNT
>>>>> 'cat /proc/net/sctp/sctp_dbg_objcnt'
>>>>>
>>>>> If unsure, say N
>>>>> +choice
>>>>> + prompt "Default SCTP cookie HMAC encoding"
>>>>> + default SCTP_COOKIE_HMAC_MD5
>>>> Should not this be SCTP_DEFAULT_COOKIE_HMAC_MD5? I just tried to
>>>> update to 3.8-rc2, and I usually build my kernel-headers with:
>>>>
>>>> yes '' | ARCH=foo make oldconfig
>>>>
>>>> and this just kept asking me for this config symbol because none
>>>> could be provided.
>>>> --
>>>> Florian
>>>>
>>> No, the config mechanism is setup to offer the user the ability to choose a
>>> default cookie hmac, alg, then optionally select any other hmac algs you would
>>> like to be made available (in the event you want to change the default at run
>>> time). When you select the default, it eables (via the select directive), the
>>> corresponding SCTP_COOKIE_HMAC_* config option, which is used in the build, and
>>> then prompts for the remaining values.
>>
>> Ok for the explanation, but this still breaks an oldconfig because
>> we do not actually propose the user with a default choice:
>>
>> choice[1-3?]: Default SCTP cookie HMAC encoding
>> 1. Enable optional MD5 hmac cookie generation
>> (SCTP_DEFAULT_COOKIE_HMAC_MD5) (NEW)
>> 2. Enable optional SHA1 hmac cookie generation
>> (SCTP_DEFAULT_COOKIE_HMAC_SHA1) (NEW)
>> 3. Use no hmac alg in SCTP cookie generation
>> (SCTP_DEFAULT_COOKIE_HMAC_NONE) (NEW)
>>
>> I do not see any difference in what I am proposed if the default
>> config symbol is SCTP_DEFAULT_COOKIE_HMAC_MD5, I can still
>> optionally choose SHA1 to be supported, and I do have a valid
>> default config for this choice. While if I keep SCTP_COOKIE_HMAC_MD5
> No, thats the problem, your old config is no longer valid with this new Kconfig
> file. Your config is telling the config utility that you want your default
> Cookie hmac to be MD5, but you've explicitly told it (via your yes "" | make
> oldconfig command), that you want SCTP_COOKIE_HMAC_MD5 to be disabled, so the
> config utility is left with no choice to prompt you again for a default hmac,
> which your command answers again by saying SCTP_DEFAULT_COOKIE_HMAC_MD5 (the
> default choice of 1). Thats your loop, you keep telling the config utility that
> you both want the default hmac to be md5, and that you don't want to allow md5
> to be an available hmac alg.
>
> Thats not a bug. I'm sorry if your old configuration needs manual updating, but
> there are no guarantees that old configurations will 'just work' in perpituity.
>
Neil
Actually, I think we have a bug in the config. Look at the thermal
driver config again. It has:
choice
prompt "Default Thermal governor"
default THERMAL_DEFAULT_GOV_STEP_WISE
config THERMAL_DEFAULT_GOV_STEP_WISE
...
config THERMAL_DEFAULT_GOV_FAIR_SHARE
...
config THERMAL_DEFAULT_GOV_USER_SPACE
...
endchoice
SCTP has:
choice
prompt "Default SCTP cookie HMAC encoding"
default SCTP_COOKIE_HMAC_MD5
config SCTP_DEFAULT_COOKIE_HMAC_MD5
...
config SCTP_DEFAULT_COOKIE_HMAC_SHA1
...
config SCTP_DEFAULT_COOKIE_HMAC_NONE
...
endchoice
See the difference? The default value of the choice statement needs to
be one of the available choices.
-vlad
> Neil
>
>> as the default I have to manually enter which option I want.
>> --
>> Florian
>> --
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