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Re: [libvirt] [PATCH v2] util: netdevbridge: fall back to ioctl from sysfs

On 11/23/18 1:42 AM, Christian Ehrhardt wrote:

On Tue, Nov 20, 2018 at 1:26 PM Daniel P. Berrangé <berrange redhat com> wrote:
On Tue, Nov 20, 2018 at 01:25:46PM +0100, Christian Ehrhardt wrote:
> There are certain cases e.g. containers where the sysfs path might
> exists, but might fail. Unfortunately the exact restrictions are only
> known to libvirt when trying to write to it so we need to try it.
> But in case it fails there is no need to fully abort, in those cases try
> to fall back to the older ioctl interface which can still work.
> That makes setting up a bridge in unprivileged LXD containers work.
> Fixes: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1802906
> Signed-off-by: Christian Ehrhardt <christian ehrhardt canonical com>
> Reported-by: Brian Candler <b candler pobox com>
> ---
>  src/util/virnetdevbridge.c | 48 +++++++++++++++++++++-----------------
>  1 file changed, 26 insertions(+), 22 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange redhat com>

Thanks for the review Daniel!

Brian (on CC) also tested a Ubuntu build with the fix applied and it worked for him in unprivileged containers.

There was no other feedback in the last three days.
But this is no area I feel entitled to push the change on my own, therefore I wanted to ping on this - ping

As long as you have commit privileges, feel free to push once there is a Reviewed-by: (unless we are in freeze).

If it makes you feel any more confident about pushing - I had personally expressed misgivings about this patch in IRC to Dan because on first read it sounded like we might be exploiting a security flaw in LXC to modify networking when it shouldn't actually be allowed, but he convinced me that the situation isn't that "bridge and tap device management via sysfs is blocked because it should be, and ioctls are accidentally left enabled when they should have been disabled", but rather that "bridge/tap device management is acceptable in this situation, but sysfs is a huge can of worms that can only be made read-only on a global basis (and *must* be made read-only due to all the other things that shouldn't be allowed in this case)". Based on that, I'm okay with the patch as well.


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