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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:
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.