containernetworking / plugins / 28881576554

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Pull #1265

github

bridge: re-generate a bridge MAC when the kernel has zeroed it out

The kernel zeroes a bridge's MAC address when its last port is removed.
The ensureAddr function pins the bridge's MAC address using the
address read when the bridge was looked up, which is before the veth
is attached. So for an existing bridge that had previously lost all its
ports, the address it tried to pin is all zeros, and pinning an all-zero
address fails with EINVAL.

In fact, this can happen in practice: an ADD that fails has its veth
cleaned up, which, if it was the first ADD, leaves the bridge portless
and hence its MAC zeroed, so the next ADD fails to pin it.

Detect that case and regenerate a random MAC address the same way the
kernel does. This is fine as it only happens if the bridge has no ports,
so no peer can hold stale state about the old address.

Signed-off-by: Tom Wieczorek <twieczorek@mirantis.com>

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