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Commit 8fe45924 authored by Teng Qin's avatar Teng Qin Committed by David S. Miller
Browse files

bpf: map_get_next_key to return first key on NULL 



When iterating through a map, we need to find a key that does not exist
in the map so map_get_next_key will give us the first key of the map.
This often requires a lot of guessing in production systems.

This patch makes map_get_next_key return the first key when the key
pointer in the parameter is NULL.

Signed-off-by: default avatarTeng Qin <qinteng@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 472ecf08

include/trace/events/bpf.h

+7 −3
Original line number Diff line number Diff line
@@ -321,11 +321,14 @@ TRACE_EVENT(bpf_map_next_key, 
		__dynamic_array(u8, key, map->key_size)

		__dynamic_array(u8, nxt, map->key_size)

		__field(bool, key_trunc)

		__field(bool, key_null)

		__field(int, ufd)

	),



	TP_fast_assign(

		if (key)

			memcpy(__get_dynamic_array(key), key, map->key_size);

		__entry->key_null = !key;

		memcpy(__get_dynamic_array(nxt), key_next, map->key_size);

		__entry->type      = map->map_type;

		__entry->key_len   = min(map->key_size, 16U);
@@ -336,8 +339,9 @@ TRACE_EVENT(bpf_map_next_key, 
	TP_printk("map type=%s ufd=%d key=[%s%s] next=[%s%s]",

		  __print_symbolic(__entry->type, __MAP_TYPE_SYM_TAB),

		  __entry->ufd,

		  __print_hex(__get_dynamic_array(key), __entry->key_len),

		  __entry->key_trunc ? " ..." : "",

		  __entry->key_null ? "NULL" : __print_hex(__get_dynamic_array(key),

							   __entry->key_len),

		  __entry->key_trunc && !__entry->key_null ? " ..." : "",

		  __print_hex(__get_dynamic_array(nxt), __entry->key_len),

		  __entry->key_trunc ? " ..." : "")

);

kernel/bpf/arraymap.c

+1 −1
Original line number Diff line number Diff line
@@ -182,7 +182,7 @@ int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value) 
static int array_map_get_next_key(struct bpf_map *map, void *key, void *next_key)

{

	struct bpf_array *array = container_of(map, struct bpf_array, map);

	u32 index = *(u32 *)key;

	u32 index = key ? *(u32 *)key : U32_MAX;

	u32 *next = (u32 *)next_key;



	if (index >= array->map.max_entries) {

kernel/bpf/hashtab.c

+5 −4
Original line number Diff line number Diff line
@@ -540,12 +540,15 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key) 
	struct hlist_nulls_head *head;

	struct htab_elem *l, *next_l;

	u32 hash, key_size;

	int i;

	int i = 0;



	WARN_ON_ONCE(!rcu_read_lock_held());



	key_size = map->key_size;



	if (!key)

		goto find_first_elem;



	hash = htab_map_hash(key, key_size);



	head = select_bucket(htab, hash);
@@ -553,10 +556,8 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key) 
	/* lookup the key */

	l = lookup_nulls_elem_raw(head, hash, key, key_size, htab->n_buckets);



	if (!l) {

		i = 0;

	if (!l)

		goto find_first_elem;

	}



	/* key was found, get next key in the same bucket */

	next_l = hlist_nulls_entry_safe(rcu_dereference_raw(hlist_nulls_next_rcu(&l->hash_node)),

kernel/bpf/syscall.c

+12 −8
Original line number Diff line number Diff line
@@ -536,6 +536,7 @@ static int map_get_next_key(union bpf_attr *attr) 
	if (IS_ERR(map))

		return PTR_ERR(map);



	if (ukey) {

		err = -ENOMEM;

		key = kmalloc(map->key_size, GFP_USER);

		if (!key)
@@ -544,6 +545,9 @@ static int map_get_next_key(union bpf_attr *attr) 
		err = -EFAULT;

		if (copy_from_user(key, ukey, map->key_size) != 0)

			goto free_key;

	} else {

		key = NULL;

	}



	err = -ENOMEM;

	next_key = kmalloc(map->key_size, GFP_USER);

tools/testing/selftests/bpf/test_maps.c

+25 −4
Original line number Diff line number Diff line
@@ -28,7 +28,7 @@ static int map_flags; 


static void test_hashmap(int task, void *data)

{

	long long key, next_key, value;

	long long key, next_key, first_key, value;

	int fd;



	fd = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value),
@@ -89,10 +89,13 @@ static void test_hashmap(int task, void *data) 
	assert(bpf_map_delete_elem(fd, &key) == -1 && errno == ENOENT);



	/* Iterate over two elements. */

	assert(bpf_map_get_next_key(fd, NULL, &first_key) == 0 &&

	       (first_key == 1 || first_key == 2));

	assert(bpf_map_get_next_key(fd, &key, &next_key) == 0 &&

	       (next_key == 1 || next_key == 2));

	       (next_key == first_key));

	assert(bpf_map_get_next_key(fd, &next_key, &next_key) == 0 &&

	       (next_key == 1 || next_key == 2));

	       (next_key == 1 || next_key == 2) &&

	       (next_key != first_key));

	assert(bpf_map_get_next_key(fd, &next_key, &next_key) == -1 &&

	       errno == ENOENT);
@@ -105,6 +108,8 @@ static void test_hashmap(int task, void *data) 


	key = 0;

	/* Check that map is empty. */

	assert(bpf_map_get_next_key(fd, NULL, &next_key) == -1 &&

	       errno == ENOENT);

	assert(bpf_map_get_next_key(fd, &key, &next_key) == -1 &&

	       errno == ENOENT);
@@ -133,7 +138,7 @@ static void test_hashmap_percpu(int task, void *data) 
{

	unsigned int nr_cpus = bpf_num_possible_cpus();

	long long value[nr_cpus];

	long long key, next_key;

	long long key, next_key, first_key;

	int expected_key_mask = 0;

	int fd, i;
@@ -193,7 +198,13 @@ static void test_hashmap_percpu(int task, void *data) 
	assert(bpf_map_delete_elem(fd, &key) == -1 && errno == ENOENT);



	/* Iterate over two elements. */

	assert(bpf_map_get_next_key(fd, NULL, &first_key) == 0 &&

	       ((expected_key_mask & first_key) == first_key));

	while (!bpf_map_get_next_key(fd, &key, &next_key)) {

		if (first_key) {

			assert(next_key == first_key);

			first_key = 0;

		}

		assert((expected_key_mask & next_key) == next_key);

		expected_key_mask &= ~next_key;
@@ -219,6 +230,8 @@ static void test_hashmap_percpu(int task, void *data) 


	key = 0;

	/* Check that map is empty. */

	assert(bpf_map_get_next_key(fd, NULL, &next_key) == -1 &&

	       errno == ENOENT);

	assert(bpf_map_get_next_key(fd, &key, &next_key) == -1 &&

	       errno == ENOENT);
@@ -264,6 +277,8 @@ static void test_arraymap(int task, void *data) 
	assert(bpf_map_lookup_elem(fd, &key, &value) == -1 && errno == ENOENT);



	/* Iterate over two elements. */

	assert(bpf_map_get_next_key(fd, NULL, &next_key) == 0 &&

	       next_key == 0);

	assert(bpf_map_get_next_key(fd, &key, &next_key) == 0 &&

	       next_key == 0);

	assert(bpf_map_get_next_key(fd, &next_key, &next_key) == 0 &&
@@ -319,6 +334,8 @@ static void test_arraymap_percpu(int task, void *data) 
	assert(bpf_map_lookup_elem(fd, &key, values) == -1 && errno == ENOENT);



	/* Iterate over two elements. */

	assert(bpf_map_get_next_key(fd, NULL, &next_key) == 0 &&

	       next_key == 0);

	assert(bpf_map_get_next_key(fd, &key, &next_key) == 0 &&

	       next_key == 0);

	assert(bpf_map_get_next_key(fd, &next_key, &next_key) == 0 &&
@@ -400,6 +417,8 @@ static void test_map_large(void) 
	       errno == E2BIG);



	/* Iterate through all elements. */

	assert(bpf_map_get_next_key(fd, NULL, &key) == 0);

	key.c = -1;

	for (i = 0; i < MAP_SIZE; i++)

		assert(bpf_map_get_next_key(fd, &key, &key) == 0);

	assert(bpf_map_get_next_key(fd, &key, &key) == -1 && errno == ENOENT);
@@ -499,6 +518,7 @@ static void test_map_parallel(void) 
	       errno == EEXIST);



	/* Check that all elements were inserted. */

	assert(bpf_map_get_next_key(fd, NULL, &key) == 0);

	key = -1;

	for (i = 0; i < MAP_SIZE; i++)

		assert(bpf_map_get_next_key(fd, &key, &key) == 0);
@@ -518,6 +538,7 @@ static void test_map_parallel(void) 


	/* Nothing should be left. */

	key = -1;

	assert(bpf_map_get_next_key(fd, NULL, &key) == -1 && errno == ENOENT);

	assert(bpf_map_get_next_key(fd, &key, &key) == -1 && errno == ENOENT);

}