linux-kernel - Re: [PATCH net 0/3] net: core: avoid unexpected situation in namespace change routine

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Message-ID: <20200324131957.GA2501774@kroah.com>
Date:   Tue, 24 Mar 2020 14:19:57 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Taehee Yoo <ap420073@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, rafael@...nel.org,
        j.vosburgh@...il.com, vfalico@...il.com, andy@...yhouse.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        mitch.a.williams@...el.com
Subject: Re: [PATCH net 0/3] net: core: avoid unexpected situation in
 namespace change routine

On Tue, Mar 24, 2020 at 12:30:41PM +0000, Taehee Yoo wrote:
> This patchset is to avoid an unexpected situation when an interface's
> namespace is being changed.
> 
> When interface's namespace is being changed, dev_change_net_namespace()
> is called. This removes and re-allocates many resources that include
> sysfs files. The "/net/class/net/<interface name>" is one of them.
> If the sysfs creation routine(device_rename()) found duplicate sysfs
> file name, it warns about it and fails. But unfortunately, at that point,
> dev_change_net_namespace() doesn't return fail because rollback cost
> is too high.
> So, the interface can't have a sysfs file.
> 
> The approach of this patchset is to find the duplicate sysfs file as
> fast as possible. If it found that, dev_change_net_namespace() returns
> fail immediately with zero rollback cost.
> 
> 1. The first patch is to add class_find_and_get_file_ns() helper function.
> That function will be used for checking the existence of duplicate
> sysfs file.
> 2. The second patch is to add netdev_class_has_file_ns().
> That function is to check whether duplicate sysfs file in
> the "/sys/class/net*" using class_find_and_get_file_ns().
> 3. The last patch is to avoid an unexpected situation.
> a) If duplicate sysfs is existing, it fails as fast as possible in
> the dev_change_net_namespace()
> b) Acquire rtnl_lock() in both bond_create_sysfs() and bond_destroy_sysfs()
> to avoid race condition.
> c) Do not remove "/sys/class/net/bonding_masters" sysfs file by
> bond_destroy_sysfs() if the file wasn't created by bond_create_sysfs().
> 
> Test commands#1:
>     ip netns add nst 
>     ip link add bonding_masters type dummy
>     modprobe bonding
>     ip link set bonding_masters netns nst 
> 
> Test commands#2:
>     ip link add bonding_masters type dummy
>     ls /sys/class/net
>     modprobe bonding
>     modprobe -rv bonding
>     ls /sys/class/net
> 
> After removing the bonding module, we can see the "bonding_masters"
> interface's sysfs will be removed.
> This is an unexpected situation.
> 
> Taehee Yoo (3):
>   class: add class_find_and_get_file_ns() helper function
>   net: core: add netdev_class_has_file_ns() helper function
>   net: core: avoid warning in dev_change_net_namespace()
> 
>  drivers/base/class.c             | 12 ++++++++++++
>  drivers/net/bonding/bond_sysfs.c | 13 ++++++++++++-
>  include/linux/device/class.h     |  4 +++-
>  include/linux/netdevice.h        |  2 +-
>  include/net/bonding.h            |  1 +
>  net/core/dev.c                   |  4 ++++
>  net/core/net-sysfs.c             | 13 +++++++++++++
>  7 files changed, 46 insertions(+), 3 deletions(-)

I don't seem to see patch 1/3 anywhere...