set->klen has to be used, not sizeof().  The latter only compares a
single register but a full check of the entire key is needed.

Example:
table ip t {
        map s {
                typeof iifname . ip saddr : verdict
                flags interval
        }
}

nft add element t s '{ "lo" . 10.0.0.0/24 : drop }' # no error, expected
nft add element t s '{ "lo" . 10.0.0.0/24 : drop }' # no error, expected
nft add element t s '{ "lo" . 10.0.0.0/8 : drop }' # bug: no error

The 3rd 'add element' should be rejected via -ENOTEMPTY, not -EEXIST,
so userspace / nft can report an error to the user.

The latter is only correct for the 2nd case (re-add of existing element).

As-is, userspace is told that the command was successful, but no elements were
added.

After this patch, 3rd command gives:
Error: Could not process rule: File exists
add element t s { "lo" . 127.0.0.0/8 . "lo"  : drop }
                  ^^^^^^^^^^^^^^^^^^^^^^^^^

Fixes: 0eb4b5ee33f2 ("netfilter: nft_set_pipapo: Separate partial and complete overlap cases on insertion")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_set_pipapo.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nft_set_pipapo.c b/net/netfilter/nft_set_pipapo.c
index 112fe46788b6..6d77a5f0088a 100644
--- a/net/netfilter/nft_set_pipapo.c
+++ b/net/netfilter/nft_set_pipapo.c
@@ -1317,8 +1317,8 @@ static int nft_pipapo_insert(const struct net *net, const struct nft_set *set,
 		else
 			dup_end = dup_key;
 
-		if (!memcmp(start, dup_key->data, sizeof(*dup_key->data)) &&
-		    !memcmp(end, dup_end->data, sizeof(*dup_end->data))) {
+		if (!memcmp(start, dup_key->data, set->klen) &&
+		    !memcmp(end, dup_end->data, set->klen)) {
 			*elem_priv = &dup->priv;
 			return -EEXIST;
 		}
-- 
2.51.2

without 'netfilter: nft_set_pipapo: fix range overlap detection':

  reject overlapping range on add       0s         [FAIL]
Returned success for add { 1.2.3.4 . 1.2.4.1-1.2.4.2 } given set:
table inet filter {
	[..]
       elements = { 1.2.3.4 . 1.2.4.1 counter packets 0 bytes 0,
                    1.2.3.0-1.2.3.4 . 1.2.4.2 counter packets 0 bytes 0 }
}

The element collides with existing ones and was not added, but kernel
returned success to userspace.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 .../net/netfilter/nft_concat_range.sh         | 45 ++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/netfilter/nft_concat_range.sh b/tools/testing/selftests/net/netfilter/nft_concat_range.sh
index ad97c6227f35..394166f224a4 100755
--- a/tools/testing/selftests/net/netfilter/nft_concat_range.sh
+++ b/tools/testing/selftests/net/netfilter/nft_concat_range.sh
@@ -29,7 +29,7 @@ TYPES="net_port port_net net6_port port_proto net6_port_mac net6_port_mac_proto
        net6_port_net6_port net_port_mac_proto_net"
 
 # Reported bugs, also described by TYPE_ variables below
-BUGS="flush_remove_add reload net_port_proto_match avx2_mismatch doublecreate"
+BUGS="flush_remove_add reload net_port_proto_match avx2_mismatch doublecreate insert_overlap"
 
 # List of possible paths to pktgen script from kernel tree for performance tests
 PKTGEN_SCRIPT_PATHS="
@@ -420,6 +420,18 @@ race_repeat	0
 perf_duration	0
 "
 
+TYPE_insert_overlap="
+display		reject overlapping range on add
+type_spec	ipv4_addr . ipv4_addr
+chain_spec	ip saddr . ip daddr
+dst		addr4
+proto		icmp
+
+race_repeat	0
+
+perf_duration	0
+"
+
 # Set template for all tests, types and rules are filled in depending on test
 set_template='
 flush ruleset
@@ -1954,6 +1966,37 @@ EOF
 	return 0
 }
 
+add_fail()
+{
+	if nft add element inet filter test "$1" 2>/dev/null ; then
+		err "Returned success for add ${1} given set:"
+		err "$(nft -a list set inet filter test )"
+		return 1
+	fi
+
+	return 0
+}
+
+test_bug_insert_overlap()
+{
+	local elements="1.2.3.4 . 1.2.4.1"
+
+	setup veth send_"${proto}" set || return ${ksft_skip}
+
+	add "{ $elements }" || return 1
+
+	elements="1.2.3.0-1.2.3.4 . 1.2.4.1"
+	add_fail "{ $elements }" || return 1
+
+	elements="1.2.3.0-1.2.3.4 . 1.2.4.2"
+	add "{ $elements }" || return 1
+
+	elements="1.2.3.4 . 1.2.4.1-1.2.4.2"
+	add_fail "{ $elements }" || return 1
+
+	return 0
+}
+
 test_reported_issues() {
 	eval test_bug_"${subtest}"
 }
-- 
2.51.2