[PATCH 4.19 064/148] bpf, lpm: Fix check prefixlen before walking trie

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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Lehner <dev@xxxxxxxxxxx>

[ Upstream commit 9b75dbeb36fcd9fc7ed51d370310d0518a387769 ]

When looking up an element in LPM trie, the condition 'matchlen ==
trie->max_prefixlen' will never return true, if key->prefixlen is larger
than trie->max_prefixlen. Consequently all elements in the LPM trie will
be visited and no element is returned in the end.

To resolve this, check key->prefixlen first before walking the LPM trie.

Fixes: b95a5c4db09b ("bpf: add a longest prefix match trie map implementation")
Signed-off-by: Florian Lehner <dev@xxxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20231105085801.3742-1-dev@xxxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/bpf/lpm_trie.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index 1a8b208f6c55..fcd3a15add41 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -194,6 +194,9 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key)
 	struct lpm_trie_node *node, *found = NULL;
 	struct bpf_lpm_trie_key *key = _key;
 
+	if (key->prefixlen > trie->max_prefixlen)
+		return NULL;
+
 	/* Start walking the trie from the root node ... */
 
 	for (node = rcu_dereference(trie->root); node;) {
-- 
2.43.0







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