netdev - Re: [PATCH] net_namespace: fixed net

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Date:   Thu, 8 Sep 2016 12:08:29 -0700
From:   Jojy Varghese <jojy.varghese@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net
Subject: Re: [PATCH] net_namespace: fixed net_device reference leak

(Updating the patch for the case when a non-loopback dev could be unregistered)

Currently during namespace cleanup, if ‘dst’ subsystem is holding
a reference to the interface in the namespace, it does not get released.
Current code first does a ’dev_hold’ on the same device followed by a
‘dev_put’ on the same device resulting in a no-op.

This change fixes this leak by assigning the initial namespace’s loopback
device to the ‘dst’ before releasing the reference to the network
device being released.

Additional reference: https://github.com/docker/docker/issues/5618

Signed-off-by: Jojy G Varghese <jojy.varghese@...il.com>
---
 net/core/dst.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/core/dst.c b/net/core/dst.c
index a1656e3..7e45593 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -433,7 +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;
+               if (dst->dev == dev_net(dst->dev)->loopback_dev)
+                       dst->dev = init_net.loopback_dev;
+               else
+                       dst->dev = dev_net(dst->dev)->loopback_dev;
+
                dev_hold(dst->dev);
                dev_put(dev);
        }
--
1.8.3.1

On Wed, Sep 7, 2016 at 6:55 PM, Jojy Varghese <jojy.varghese@...il.com> wrote:
> During namespace cleanup, if ‘dst’ subsystem is holding
> a reference to the loopback interface in the namespace, it does not get
> released. This is because in the case where the net_device held by 'dst'
> is same as the namespace's loopback net_device, current code first
> does a ’dev_hold’ on the same device followed by a ‘dev_put’ on the
> same device resulting in a no-op.
>
> This change fixes this leak by assigning the initial namespace’s loopback
> device to the ‘dst’’ before releasing the reference to the network device
> being unregistered.
>
> Additional reference: https://github.com/docker/docker/issues/5618
>
> Signed-off-by: Jojy G Varghese <jojy.varghese@...il.com>
> ---
>  net/core/dst.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/dst.c b/net/core/dst.c
> index a1656e3..a18e8ea 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -433,7 +433,7 @@ 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;
> +               dst->dev = init_net.loopback_dev;
>                 dev_hold(dst->dev);
>                 dev_put(dev);
>         }
> --
> 1.8.3.1



-- 
Jojy G Varghese