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Date: Mon, 24 Aug 2020 13:39:37 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: netfilter-devel@...r.kernel.org
Cc: davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org
Subject: [PATCH 2/6] netfilter: nft_set_rbtree: Handle outcomes of tree rotations in overlap detection
From: Stefano Brivio <sbrivio@...hat.com>
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@....eu>
Bugzilla: https://bugzilla.netfilter.org/show_bug.cgi?id=1449
Cc: <stable@...r.kernel.org> # 5.6.x
Fixes: 7c84d41416d8 ("netfilter: nft_set_rbtree: Detect partial overlaps on insertion")
Signed-off-by: Stefano Brivio <sbrivio@...hat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
net/netfilter/nft_set_rbtree.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 4b2834fd17b2..27668f4e44ea 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -238,21 +238,27 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
*
* b1. _ _ __>| !_ _ __| (insert end before existing start)
* b2. _ _ ___| !_ _ _>| (insert end after existing start)
- * b3. _ _ ___! >|_ _ __| (insert start after existing end)
+ * b3. _ _ ___! >|_ _ __| (insert start after existing end, as a leaf)
+ * '--' no nodes falling in this range
+ * b4. >|_ _ ! (insert start before existing start)
*
* Case a3. resolves to b3.:
* - if the inserted start element is the leftmost, because the '0'
* element in the tree serves as end element
- * - otherwise, if an existing end is found. Note that end elements are
- * always inserted after corresponding start elements.
+ * - otherwise, if an existing end is found immediately to the left. If
+ * there are existing nodes in between, we need to further descend the
+ * tree before we can conclude the new start isn't causing an overlap
+ *
+ * or to b4., which, preceded by a3., means we already traversed one or
+ * more existing intervals entirely, from the right.
*
* For a new, rightmost pair of elements, we'll hit cases b3. and b2.,
* in that order.
*
* The flag is also cleared in two special cases:
*
- * b4. |__ _ _!|<_ _ _ (insert start right before existing end)
- * b5. |__ _ >|!__ _ _ (insert end right after existing start)
+ * b5. |__ _ _!|<_ _ _ (insert start right before existing end)
+ * b6. |__ _ >|!__ _ _ (insert end right after existing start)
*
* which always happen as last step and imply that no further
* overlapping is possible.
@@ -272,7 +278,7 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
if (nft_rbtree_interval_start(new)) {
if (nft_rbtree_interval_end(rbe) &&
nft_set_elem_active(&rbe->ext, genmask) &&
- !nft_set_elem_expired(&rbe->ext))
+ !nft_set_elem_expired(&rbe->ext) && !*p)
overlap = false;
} else {
overlap = nft_rbtree_interval_end(rbe) &&
@@ -288,10 +294,9 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
nft_set_elem_active(&rbe->ext,
genmask) &&
!nft_set_elem_expired(&rbe->ext);
- } else if (nft_rbtree_interval_end(rbe) &&
- nft_set_elem_active(&rbe->ext, genmask) &&
+ } else if (nft_set_elem_active(&rbe->ext, genmask) &&
!nft_set_elem_expired(&rbe->ext)) {
- overlap = true;
+ overlap = nft_rbtree_interval_end(rbe);
}
} else {
if (nft_rbtree_interval_end(rbe) &&
--
2.20.1
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