netdev - Re: [PATCH net] ipv6: dad: don't remove dynamic addresses if link is down

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Message-Id: <20170703.015438.1191171935015250152.davem@davemloft.net>
Date:   Mon, 03 Jul 2017 01:54:38 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org, hannes@...essinduktion.org
Subject: Re: [PATCH net] ipv6: dad: don't remove dynamic addresses if link
 is down

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Thu, 29 Jun 2017 16:56:54 +0200

> Currently, when the link for $DEV is down, this command succeeds but the
> address is removed immediately by DAD (1):
> 
>     ip addr add 1111::12/64 dev $DEV valid_lft 3600 preferred_lft 1800
> 
> In the same situation, this will succeed and not remove the address (2):
> 
>     ip addr add 1111::12/64 dev $DEV
>     ip addr change 1111::12/64 dev $DEV valid_lft 3600 preferred_lft 1800
> 
> The comment in addrconf_dad_begin() when !IF_READY makes it look like
> this is the intended behavior, but doesn't explain why:
> 
>      * If the device is not ready:
>      * - keep it tentative if it is a permanent address.
>      * - otherwise, kill it.
> 
> We clearly cannot prevent userspace from doing (2), but we can make (1)
> work consistently with (2).
> 
> addrconf_dad_stop() is only called in two cases: if DAD failed, or to
> skip DAD when the link is down. In that second case, the fix is to avoid
> deleting the address, like we already do for permanent addresses.
> 
> Fixes: 3c21edbd1137 ("[IPV6]: Defer IPv6 device initialization until the link becomes ready.")
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>

Applied and queued up for -stable, thanks.