netdev - Re: [PATCH net-next v4 2/6] net: bridge: Set strict_start_type for br

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Date: Thu, 21 Sep 2023 09:23:46 +0200
From: Johannes Nixdorf <jnixdorf-oss@....de>
To: Nikolay Aleksandrov <razor@...ckwall.org>
Cc: "David S. Miller" <davem@...emloft.net>, Andrew Lunn <andrew@...n.ch>,
	David Ahern <dsahern@...il.com>, Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Ido Schimmel <idosch@...dia.com>, Jakub Kicinski <kuba@...nel.org>,
	Oleksij Rempel <linux@...pel-privat.de>,
	Paolo Abeni <pabeni@...hat.com>, Roopa Prabhu <roopa@...dia.com>,
	Shuah Khan <shuah@...nel.org>,
	Vladimir Oltean <vladimir.oltean@....com>,
	bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v4 2/6] net: bridge: Set strict_start_type for
 br_policy

On Wed, Sep 20, 2023 at 01:46:02PM +0300, Nikolay Aleksandrov wrote:
> On 9/19/23 11:12, Johannes Nixdorf wrote:
> > Set any new attributes added to br_policy to be parsed strictly, to
> > prevent userspace from passing garbage.
> > 
> > Signed-off-by: Johannes Nixdorf <jnixdorf-oss@....de>
> > ---
> >   net/bridge/br_netlink.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> > index 10f0d33d8ccf..505683ef9a26 100644
> > --- a/net/bridge/br_netlink.c
> > +++ b/net/bridge/br_netlink.c
> > @@ -1229,6 +1229,8 @@ static size_t br_port_get_slave_size(const struct net_device *brdev,
> >   }
> >   static const struct nla_policy br_policy[IFLA_BR_MAX + 1] = {
> > +	[IFLA_BR_UNSPEC]	= { .strict_start_type =
> > +				    IFLA_BR_MCAST_QUERIER_STATE + 1 },
> >   	[IFLA_BR_FORWARD_DELAY]	= { .type = NLA_U32 },
> >   	[IFLA_BR_HELLO_TIME]	= { .type = NLA_U32 },
> >   	[IFLA_BR_MAX_AGE]	= { .type = NLA_U32 },
> > 
> 
> instead of IFLA_BR_MCAST_QUERIER_STATE + 1, why not move around the patch
> and just use the new attribute name?
> These are uapi, they won't change.

I wanted to avoid having a state between the two commits where the new
attributes are already added, but not yet strictly verified. Otherwise
they would present a slightly different UAPI at that one commit boundary
than after this commit.

This is also not the only place in the kernel where strict_start_type
is specified that way. See e.g. commit c00041cf1cb8 ("net: bridge: Set
strict_start_type at two policies"), even though that seems mostly be
done to turn on strict_start_type preemtively, not in the same series
that adds the new attribute.