netdev - Re: [PATCH v3 net-next 10/12] net: bonding: ensure .ndo_get

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Date:   Thu, 7 Jan 2021 12:18:28 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        George McCollister <george.mccollister@...il.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Arnd Bergmann <arnd@...db.de>, Taehee Yoo <ap420073@...il.com>,
        Jiri Pirko <jiri@...lanox.com>, Florian Westphal <fw@...len.de>
Subject: Re: [PATCH v3 net-next 10/12] net: bonding: ensure .ndo_get_stats64
 can sleep

On Thu, Jan 7, 2021 at 10:51 AM Vladimir Oltean <olteanv@...il.com> wrote:
>
> From: Vladimir Oltean <vladimir.oltean@....com>
>
>

-
>  static void bond_get_stats(struct net_device *bond_dev,
>                            struct rtnl_link_stats64 *stats)
>  {
>         struct bonding *bond = netdev_priv(bond_dev);
> -       struct rtnl_link_stats64 temp;
> -       struct list_head *iter;
> -       struct slave *slave;
> -       int nest_level = 0;
> +       struct rtnl_link_stats64 *dev_stats;
> +       struct net_device **slaves;
> +       int i, res, num_slaves;
>
> +       res = bond_get_slave_arr(bond, &slaves, &num_slaves);
> +       if (res) {
> +               netdev_err(bond->dev,
> +                          "failed to allocate memory for slave array\n");
> +               return;
> +       }
>

What a mess really.

You chose to keep the assumption that ndo_get_stats() would not fail,
since we were providing the needed storage from callers.

If ndo_get_stats() are now allowed to sleep, and presumably allocate
memory, we need to make sure
we report potential errors back to the user.

I think your patch series is mostly good, but I would prefer not
hiding errors and always report them to user space.
And no, netdev_err() is not appropriate, we do not want tools to look
at syslog to guess something went wrong.

Last point about drivers having to go to slow path, talking to
firmware : Make sure that malicious/innocent users
reading /proc/net/dev from many threads in parallel wont brick these devices.

Maybe they implicitly _relied_ on the fact that firmware was gently
read every second and results were cached from a work queue or
something.

Thanks.