Further things that someone may want to read/try (if the below is true),
https://en.wikipedia.org/wiki/ReDoS
Joshua Harlow wrote:
Just the paranoid person in me, but is it safe to say that the filter
that you are showing here does not come from user text?
Ie these two lines don't come from a user input directly (without going
through some filter) do they?
https://github.com/openstack/nova/blob/16.0.0/nova/compute/api.py#L2458-L2459
From reading it seems like perhaps they do come at least partially from
a user, so I am hoping that its not possible for a user to present a
'ip' that is really a complicated regex that takes a long time to
compile (and therefore can DOS the nova-api component); but I don't know
the surrounding code so I might be wrong...
Just wondering :-/
-Josh
Matt Riedemann wrote:
Nova has had this long-standing known performance issue if you're
filtering a large number of instances by IP. The instance IPs are stored
in a JSON blob in the database so we don't do filtering in SQL. We pull
the instances out of the database, deserialize the JSON and then apply a
regex filter match in the nova-api python code.
At the Queens PTG we talked about possible ways to fix this and came up
with this nova spec:
https://specs.openstack.org/openstack/nova-specs/specs/queens/approved/improve-filter-instances-by-ip-performance.html
The idea is to have nova get ports from neutron and apply the IP filter
in neutron to whittle down the ports, then from that list of ports get
the instances to pull out of the nova database.
One issue that has come up with this is neutron does not currently
support regex filters when listing ports. There is an RFE for adding
that:
https://bugs.launchpad.net/neutron/+bug/1718605
The proposed neutron implementation is to just do SQL LIKE substring
matching in the database.
However, one issue that has come up is that the compute API accepts a
python regex filter and uses re.match():
https://github.com/openstack/nova/blob/16.0.0/nova/compute/api.py#L2469
At least one good thing about that is match() only matches from the
beginning of the string unlike search().
So for example I can filter on "192.16.*[1-5]$" if I wanted to, but
that's not going to work with just a LIKE substring filter in SQL.
The question is, does anyone actually do more than basic substring
matching with the IP filter today? Because if we started using neutron,
that behavior would be broken. We've never actually documented the match
restrictions on the IP filter, but that's not a good reason to break it.
One option is to make this configurable such that deployments which rely
on the complicated pattern matching can just use the existing nova code
despite performance issues. However, that's not interoperable, I hate
config-driven API behavior, and it would mean maintaining two code paths
in nova, which is also terrible.
I was trying to think of a way to determine if the IP filter passed to
nova is basic or a complicated pattern match and let us decide that way,
but I'm not sure if there are good ways to detect that - maybe by simply
looking for special characters like (, ), - and $? But then there is []
and we have an IPv6 filter, so that gets messy too...
For now I'd just like to know if people rely on the regex match or not.
Other ideas on how to handle this are appreciated.
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