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Subject[PATCH net-next v3 0/8] Make /sys/class/net per net namespace objects belong to container
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This is a revival of an older patch set from Dmitry Torokhov:

https://lore.kernel.org/lkml/1471386795-32918-1-git-send-email-dmitry.torokhov@gmail.com/

My submission of v2 is here:

https://lore.kernel.org/lkml/1531497949-1766-1-git-send-email-tyhicks@canonical.com/

Here's Dmitry's description:

There are objects in /sys hierarchy (/sys/class/net/) that logically
belong to a namespace/container. Unfortunately all sysfs objects start
their life belonging to global root, and while we could change
ownership manually, keeping tracks of all objects that come and go is
cumbersome. It would be better if kernel created them using correct
uid/gid from the beginning.

This series changes kernfs to allow creating object's with arbitrary
uid/gid, adds get_ownership() callback to ktype structure so subsystems
could supply their own logic (likely tied to namespace support) for
determining ownership of kobjects, and adjusts sysfs code to make use
of this information. Lastly net-sysfs is adjusted to make sure that
objects in net namespace are owned by the root user from the owning
user namespace.

Note that we do not adjust ownership of objects moved into a new
namespace (as when moving a network device into a container) as
userspace can easily do it.

I'm reviving this patch set because we would like this feature for
system containers. One specific use case that we have is that libvirt is
unable to configure its bridge device inside of a system container due
to the bridge files in /sys/class/net/ being owned by init root instead
of container root. The last two patches in this set are patches that
I've added to Dmitry's original set to allow such configuration of the
bridge device.

Eric had previously provided feedback that he didn't favor these changes
affecting all layers of the stack and that most of the changes could
remain local to drivers/base/core.c. That feedback is certainly sensible
but I wanted to send out v2 of the patch set without making that large
of a change since quite a bit of time has passed and the bridge changes
in the last patch of this set shows that not all of the changes will be
local to drivers/base/core.c. I'm happy to make the changes if the
original request still stands.

* Changes since v2:
- Added my Co-Developed-by and Signed-off-by tags to all of Dmitry's
patches that I've modified
- Patch 1 received build failure fixes in
arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
- Patch 2 was updated to drop the declaration of sysfs_add_file() from
sysfs.h since the patch removed all other uses of the function
- Patch 5 is a new patch that prevents tx_maxrate from being written
to from inside of a container
+ Maybe I'm being too cautious here but the restriction can always
be loosened up later
- Patches 6 and 7 were updated to make net_ns_get_ownership() always
initialize uid and gid, even when the network namespace is NULL, so
that it isn't a dangerous function to reuse
+ Requested by Christian Brauner
- I've looked at all sysfs attributes affected by this patch set and
feel comfortable about the changes. There are quite a few affected
attributes that don't have any capable()/ns_capable() checks in
their store operations (per_bond_attrs, at91_sysfs_attrs,
sysfs_grcan_attrs, ican3_sysfs_attrs, cdc_ncm_sysfs_attrs,
qmi_wwan_sysfs_attrs) but I think this is acceptable. It means that
container root, rather than specifically CAP_NET_ADMIN inside of the
network namespace that the device belongs to, can write to those
device attributes. It's the same situation that those devices have
today in that init root is able to write to the attributes without
necessarily having CAP_NET_ADMIN. I think that this should probably
be fixed in order to be consistent with what netdev_store() does by
verifying CAP_NET_ADMIN in the network namespace but that it doesn't
need to happen in this patch set.

Thanks!

Tyler

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