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Date:   Thu, 21 Sep 2023 09:23:46 +0200
From:   Johannes Nixdorf <jnixdorf-oss@avm.de>
To:     Nikolay Aleksandrov <razor@blackwall.org>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Andrew Lunn <andrew@lunn.ch>, David Ahern <dsahern@gmail.com>,
        Eric Dumazet <edumazet@google.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Ido Schimmel <idosch@nvidia.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Oleksij Rempel <linux@rempel-privat.de>,
        Paolo Abeni <pabeni@redhat.com>,
        Roopa Prabhu <roopa@nvidia.com>, Shuah Khan <shuah@kernel.org>,
        Vladimir Oltean <vladimir.oltean@nxp.com>,
        bridge@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH net-next v4 2/6] net: bridge: Set strict_start_type for
 br_policy
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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@avm.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.