226a88de47
Checks for partial overlaps on insertion assume that end elements
are always descendant nodes of their corresponding start, because
they are inserted later. However, this is not the case if a
previous delete operation caused a tree rotation as part of
rebalancing.
Taking the issue reported by Andreas Fischer as an example, if we
omit delete operations, the existing procedure works because,
equivalently, we are inserting a start item with value 40 in the
this region of the red-black tree with single-sized intervals:
overlap flag
10 (start)
/ \ false
20 (start)
/ \ false
30 (start)
/ \ false
60 (start)
/ \ false
50 (end)
/ \ false
20 (end)
/ \ false
40 (start)
if we now delete interval 30 - 30, the tree can be rearranged in
a way similar to this (note the rotation involving 50 - 50):
overlap flag
10 (start)
/ \ false
20 (start)
/ \ false
25 (start)
/ \ false
70 (start)
/ \ false
50 (end)
/ \ true (from rule a1.)
50 (start)
/ \ true
40 (start)
and we traverse interval 50 - 50 from the opposite direction
compared to what was expected.
To deal with those cases, add a start-before-start rule, b4.,
that covers traversal of existing intervals from the right.
We now need to restrict start-after-end rule b3. to cases
where there are no occurring nodes between existing start and
end elements, because addition of rule b4. isn't sufficient to
ensure that the pre-existing end element we encounter while
descending the tree corresponds to a start element of an
interval that we already traversed entirely.
Different types of overlap detection on trees with rotations
resulting from re-balancing will be covered by nft test case
sets/0044interval_overlap_1.
Reported-by: Andreas Fischer <netfilter@d9c.eu>
Bugzilla: https://bugzilla.netfilter.org/show_bug.cgi?id=1449
Cc: <stable@vger.kernel.org> # 5.6.x
Fixes: 7c84d41416d8 ("netfilter: nft_set_rbtree: Detect partial overlaps on insertion")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Linux kernel
============
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