[PATCH AUTOSEL 5.4 26/32] netfilter: nft_set_rbtree: Detect partial overlaps on insertion

Sasha Levin
2020-04-07T00:05:55Z

From: Stefano Brivio <sbrivio@redhat.com>

[ Upstream commit 7c84d41416d836ef7e533bd4d64ccbdf40c5ac70 ]

...and return -ENOTEMPTY to the front-end in this case, instead of
proceeding. Currently, nft takes care of checking for these cases
and not sending them to the kernel, but if we drop the set_overlap()
call in nft we can end up in situations like:

# nft add table t
# nft add set t s '{ type inet_service ; flags interval ; }'
# nft add element t s '{ 1 - 5 }'
# nft add element t s '{ 6 - 10 }'
# nft add element t s '{ 4 - 7 }'
# nft list set t s
table ip t {
set s {
type inet_service
flags interval
elements = { 1-3, 4-5, 6-7 }
}
}

This change has the primary purpose of making the behaviour
consistent with nft_set_pipapo, but is also functional to avoid
inconsistent behaviour if userspace sends overlapping elements for
any reason.

v2: When we meet the same key data in the tree, as start element while
inserting an end element, or as end element while inserting a start
element, actually check that the existing element is active, before
resetting the overlap flag (Pablo Neira Ayuso)

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nft_set_rbtree.c | 70 ++++++++++++++++++++++++++++++++--
1 file changed, 67 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 95fcba34bfd35..996fd9dc6160c 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -213,8 +213,43 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
u8 genmask = nft_genmask_next(net);
struct nft_rbtree_elem *rbe;
struct rb_node *parent, **p;
+ bool overlap = false;
int d;

+ /* Detect overlaps as we descend the tree. Set the flag in these cases:
+ *
+ * a1. |__ _ _? >|__ _ _ (insert start after existing start)
+ * a2. _ _ __>| ?_ _ __| (insert end before existing end)
+ * a3. _ _ ___| ?_ _ _>| (insert end after existing end)
+ * a4. >|__ _ _ _ _ __| (insert start before existing end)
+ *
+ * and clear it later on, as we eventually reach the points indicated by
+ * '?' above, in the cases described below. We'll always meet these
+ * later, locally, due to tree ordering, and overlaps for the intervals
+ * that are the closest together are always evaluated last.
+ *
+ * b1. |__ _ _! >|__ _ _ (insert start after existing end)
+ * b2. _ _ __>| !_ _ __| (insert end before existing start)
+ * b3. !_____>| (insert end after existing start)
+ *
+ * Case a4. resolves to b1.:
+ * - 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.
+ *
+ * For a new, rightmost pair of elements, we'll hit cases b1. and b3.,
+ * 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)
+ *
+ * which always happen as last step and imply that no further
+ * overlapping is possible.
+ */
+
parent = NULL;
p = &priv->root.rb_node;
while (*p != NULL) {
@@ -223,17 +258,42 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
d = memcmp(nft_set_ext_key(&rbe->ext),
nft_set_ext_key(&new->ext),
set->klen);
- if (d < 0)
+ if (d < 0) {
p = &parent->rb_left;
- else if (d > 0)
+
+ if (nft_rbtree_interval_start(new)) {
+ overlap = nft_rbtree_interval_start(rbe) &&
+ nft_set_elem_active(&rbe->ext,
+ genmask);
+ } else {
+ overlap = nft_rbtree_interval_end(rbe) &&
+ nft_set_elem_active(&rbe->ext,
+ genmask);
+ }
+ } else if (d > 0) {
p = &parent->rb_right;
- else {
+
+ if (nft_rbtree_interval_end(new)) {
+ overlap = nft_rbtree_interval_end(rbe) &&
+ nft_set_elem_active(&rbe->ext,
+ genmask);
+ } else if (nft_rbtree_interval_end(rbe) &&
+ nft_set_elem_active(&rbe->ext, genmask)) {
+ overlap = true;
+ }
+ } else {
if (nft_rbtree_interval_end(rbe) &&
nft_rbtree_interval_start(new)) {
p = &parent->rb_left;
+
+ if (nft_set_elem_active(&rbe->ext, genmask))
+ overlap = false;
} else if (nft_rbtree_interval_start(rbe) &&
nft_rbtree_interval_end(new)) {
p = &parent->rb_right;
+
+ if (nft_set_elem_active(&rbe->ext, genmask))
+ overlap = false;
} else if (nft_set_elem_active(&rbe->ext, genmask)) {
*ext = &rbe->ext;
return -EEXIST;
@@ -242,6 +302,10 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
}
}
}
+
+ if (overlap)
+ return -ENOTEMPTY;
+
rb_link_node_rcu(&new->node, parent, p);
rb_insert_color(&new->node, &priv->root);
return 0;
--
2.20.1