netdev - Re: [PATCH net] ipv6: set all.accept

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Message-ID: <CAGnkfhy6si-sJEZ3_FbrqakeCY3sz=PZBdBbw-iKOGb+LCV-kA@mail.gmail.com>
Date:   Mon, 13 Nov 2017 15:28:21 +0100
From:   Matteo Croce <mcroce@...hat.com>
To:     Erik Kline <ek@...gle.com>
Cc:     Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Stefano Brivio <sbrivio@...hat.com>,
        Maciej Żenczykowski <maze@...gle.com>
Subject: Re: [PATCH net] ipv6: set all.accept_dad to 0 by default

On Mon, Nov 13, 2017 at 3:21 PM, Erik Kline <ek@...gle.com> wrote:
> Should we consider rolling back the patch that caused this?
> "accept_dad = 1" is the proper IETF-expected default behaviour.
>
> Alternatively, if we really want to make all, default, and ifname
> useful perhaps we need to investigate a tristate option (for currently
> boolean values, at least).  -1 could mean no preference, for example.
>
> On 13 November 2017 at 13:45, Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
>> The commit a2d3f3e33853 modifies the way to disable dad on an interface.
>> Before the patch, setting <iface>.accept_dad to 0 was enough to disable it.
>> Because all.accept_dad is set to 1 by default, after the patch, the user
>> needs to set both all.accept_dad and <iface>.accept_dad to 0 to disable it.
>>
>> This is not backward compatible. When a user updates its kernel, the dad
>> may be enabled by error.
>>
>> Let's set all.accept_dad to 0 by default to restore the previous behavior.
>>
>> Fixes: a2d3f3e33853 ("ipv6: fix net.ipv6.conf.all.accept_dad behaviour for real")
>> CC: Stefano Brivio <sbrivio@...hat.com>
>> CC: Matteo Croce <mcroce@...hat.com>
>> CC: Erik Kline <ek@...gle.com>
>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>> ---
>>  net/ipv6/addrconf.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
>> index 8a1c846d3df9..ef5b61507b9a 100644
>> --- a/net/ipv6/addrconf.c
>> +++ b/net/ipv6/addrconf.c
>> @@ -231,7 +231,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
>>         .proxy_ndp              = 0,
>>         .accept_source_route    = 0,    /* we do not accept RH0 by default. */
>>         .disable_ipv6           = 0,
>> -       .accept_dad             = 1,
>> +       .accept_dad             = 0,
>>         .suppress_frag_ndisc    = 1,
>>         .accept_ra_mtu          = 1,
>>         .stable_secret          = {
>> --
>> 2.13.2
>>

Another way could be putting the "all" and per interface handlers in
logical AND.
The fact is before the patch, the "all" handler really was a noop.
What do you think?

-- 
Matteo Croce
per aspera ad upstream