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netfilter: nft_set_rbtree: Drop spurious condition for overlap detection on insertion 

Case a1. for overlap detection in __nft_rbtree_insert() is not a valid
one: start-after-start is not needed to detect any type of interval
overlap and it actually results in a false positive if, while
descending the tree, this is the only step we hit after starting from
the root.

This introduced a regression, as reported by Pablo, in Python tests
cases ip/ip.t and ip/numgen.t:

  ip/ip.t: ERROR: line 124: add rule ip test-ip4 input ip hdrlength vmap { 0-4 : drop, 5 : accept, 6 : continue } counter: This rule should not have failed.
  ip/numgen.t: ERROR: line 7: add rule ip test-ip4 pre dnat to numgen inc mod 10 map { 0-5 : 192.168.10.100, 6-9 : 192.168.20.200}: This rule should not have failed.

Drop case a1. and renumber others, so that they are a bit clearer. In
order for these diagrams to be readily understandable, a bigger rework
is probably needed, such as an ASCII art of the actual rbtree (instead
of a flattened version).

Shell script test sets/0044interval_overlap_0 should cover all
possible cases for false negatives, so I consider that test case still
sufficient after this change.

v2: Fix comments for cases a3. and b3.

Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Fixes: 7c84d41416 ("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>
This commit is contained in:
Stefano Brivio 2020-04-01 17:14:38 +02:00 committed by Pablo Neira Ayuso
parent 0452800f6d
commit 72239f2795
1 changed files with 11 additions and 12 deletions
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23
net/netfilter/nft_set_rbtree.c
View File

@ -218,27 +218,26 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
/* 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)
* a1. _ _ __>| ?_ _ __| (insert end before existing end)
* a2. _ _ ___| ?_ _ _>| (insert end after existing end)
* a3. _ _ ___? >|_ _ __| (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)
* b1. _ _ __>| !_ _ __| (insert end before existing start)
* b2. _ _ ___| !_ _ _>| (insert end after existing start)
* b3. _ _ ___! >|_ _ __| (insert start after existing end)
*
* Case a4. resolves to b1.:
* 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.
*
* For a new, rightmost pair of elements, we'll hit cases b1. and b3.,
* 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:
@ -262,9 +261,9 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
p = &parent->rb_left;
if (nft_rbtree_interval_start(new)) {
overlap = nft_rbtree_interval_start(rbe) &&
nft_set_elem_active(&rbe->ext,
genmask);
if (nft_rbtree_interval_end(rbe) &&
nft_set_elem_active(&rbe->ext, genmask))
overlap = false;
} else {
overlap = nft_rbtree_interval_end(rbe) &&
nft_set_elem_active(&rbe->ext,