Linux Ethernet Bridging - Sep 2023 - [Bridge] [PATCH net-next v4 2/6] net: bridge: Set strict_start_type for br_policy

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 at 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.

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 at 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.