Re: [PATCH net V3] net: reevalulate autoflowlabel setting after sysctl setting

[David Miller <davem@davemloft.net>]

From: Shaohua Li <shli@kernel.org>
Date: Wed, 20 Dec 2017 12:10:21 -0800

> From: Shaohua Li <shli@fb.com>
> 
> sysctl.ip6.auto_flowlabels is default 1. In our hosts, we set it to 2.
> If sockopt doesn't set autoflowlabel, outcome packets from the hosts are
> supposed to not include flowlabel. This is true for normal packet, but
> not for reset packet.
> 
> The reason is ipv6_pinfo.autoflowlabel is set in sock creation. Later if
> we change sysctl.ip6.auto_flowlabels, the ipv6_pinfo.autoflowlabel isn't
> changed, so the sock will keep the old behavior in terms of auto
> flowlabel. Reset packet is suffering from this problem, because reset
> packet is sent from a special control socket, which is created at boot
> time. Since sysctl.ipv6.auto_flowlabels is 1 by default, the control
> socket will always have its ipv6_pinfo.autoflowlabel set, even after
> user set sysctl.ipv6.auto_flowlabels to 1, so reset packset will always
> have flowlabel. Normal sock created before sysctl setting suffers from
> the same issue. We can't even turn off autoflowlabel unless we kill all
> socks in the hosts.
> 
> To fix this, if IPV6_AUTOFLOWLABEL sockopt is used, we use the
> autoflowlabel setting from user, otherwise we always call
> ip6_default_np_autolabel() which has the new settings of sysctl.
> 
> Note, this changes behavior a little bit. Before commit 42240901f7c4
> (ipv6: Implement different admin modes for automatic flow labels), the
> autoflowlabel behavior of a sock isn't sticky, eg, if sysctl changes,
> existing connection will change autoflowlabel behavior. After that
> commit, autoflowlabel behavior is sticky in the whole life of the sock.
> With this patch, the behavior isn't sticky again.
> 
> Cc: Martin KaFai Lau <kafai@fb.com>
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Tom Herbert <tom@quantonium.net>
> Signed-off-by: Shaohua Li <shli@fb.com>

This looks a lot better, applied, thanks.