netdev - Re: [PATCH] net_namespace: fixed net

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Message-ID: <1473378685.18970.22.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 08 Sep 2016 16:51:25 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jojy Varghese <jojy.varghese@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] net_namespace: fixed net_device reference leak

On Thu, 2016-09-08 at 16:33 -0700, Jojy Varghese wrote:
> Sorry last patch was just the delta over my original patch. Here is
> the complete patch:
> 
> ---
>  net/core/dst.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/dst.c b/net/core/dst.c
> index a1656e3..f63027e 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -433,8 +433,11 @@ static void dst_ifdown(struct dst_entry *dst,
> struct net_device *dev,
>                 dst->input = dst_discard;
>                 dst->output = dst_discard_out;
>         } else {
> -               dst->dev = dev_net(dst->dev)->loopback_dev;
> -               dev_hold(dst->dev);
> +               if (dst->dev != dev_net(dst->dev)->loopback_dev) {
> +                       dst->dev = dev_net(dst->dev)->loopback_dev;
> +                       dev_hold(dst->dev);
> +               }
> +
>                 dev_put(dev);
>         }
>  }

This is complete garbage, now we have a dst somewhere in the system,
pointing to a device that might have been freed.

Crash might happen when dst->dev is used later.