bpf, lpm: fix lookup bug in map_delete_elem

alban · borkmann · commit 7c0cdf0b3940 · 2019-02-22T16:17:53.000+01:00
trie_delete_elem() was deleting an entry even though it was not matching if the prefixlen was correct. This patch adds a check on matchlen. Reproducer: $ sudo bpftool map create /sys/fs/bpf/mylpm type lpm_trie key 8 value 1 entries 128 name mylpm flags 1 $ sudo bpftool map update pinned /sys/fs/bpf/mylpm key hex 10 00 00 00 aa bb cc dd value hex 01 $ sudo bpftool map dump pinned /sys/fs/bpf/mylpm key: 10 00 00 00 aa bb cc dd value: 01 Found 1 element $ sudo bpftool map delete pinned /sys/fs/bpf/mylpm key hex 10 00 00 00 ff ff ff ff $ echo $? 0 $ sudo bpftool map dump pinned /sys/fs/bpf/mylpm Found 0 elements A similar reproducer is added in the selftests. Without the patch: $ sudo ./tools/testing/selftests/bpf/test_lpm_map test_lpm_map: test_lpm_map.c:485: test_lpm_delete: Assertion `bpf_map_delete_elem(map_fd, key) == -1 && errno == ENOENT' failed. Aborted With the patch: test_lpm_map runs without errors. Fixes: e454cf5 ("bpf: Implement map_delete_elem for BPF_MAP_TYPE_LPM_TRIE") Cc: Craig Gallek <kraig@google.com> Signed-off-by: Alban Crequy <alban@kinvolk.io> Acked-by: Craig Gallek <kraig@google.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
@@ -471,6 +471,7 @@ static int trie_delete_elem(struct bpf_map *map, void *_key)
 	}
 
 	if (!node || node->prefixlen != key->prefixlen ||
+	    node->prefixlen != matchlen ||
 	    (node->flags & LPM_TREE_NODE_FLAG_IM)) {
 		ret = -ENOENT;
 		goto out;
diff --git a/tools/testing/selftests/bpf/test_lpm_map.c b/tools/testing/selftests/bpf/test_lpm_map.c
@@ -474,6 +474,16 @@ static void test_lpm_delete(void)
 	assert(bpf_map_lookup_elem(map_fd, key, &value) == -1 &&
 		errno == ENOENT);
 
+	key->prefixlen = 30; // unused prefix so far
+	inet_pton(AF_INET, "192.255.0.0", key->data);
+	assert(bpf_map_delete_elem(map_fd, key) == -1 &&
+		errno == ENOENT);
+
+	key->prefixlen = 16; // same prefix as the root node
+	inet_pton(AF_INET, "192.255.0.0", key->data);
+	assert(bpf_map_delete_elem(map_fd, key) == -1 &&
+		errno == ENOENT);
+
 	/* assert initial lookup */
 	key->prefixlen = 32;
 	inet_pton(AF_INET, "192.168.0.1", key->data);

Original file line number	Diff line number	Diff line change
`@@ -471,6 +471,7 @@ static int trie_delete_elem(struct bpf_map map, void _key)`
`471`	`471`	`}`
`472`	`472`
`473`	`473`	`if (!node \|\| node->prefixlen != key->prefixlen \|\|`
	`474`	`+ node->prefixlen != matchlen \|\|`
`474`	`475`	`(node->flags & LPM_TREE_NODE_FLAG_IM)) {`
`475`	`476`	`ret = -ENOENT;`
`476`	`477`	`goto out;`