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bpf: map_get_next_key to return first key on NULL
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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: Teng Qin <qinteng@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@palmtenor @davem330
palmtenor authored and davem330 committed Apr 25, 2017
1 parent 472ecf0 commit 8fe4592
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Showing 5 changed files with 50 additions and 20 deletions.
10 changes: 7 additions & 3 deletions include/trace/events/bpf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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(
memcpy(__get_dynamic_array(key), key, map->key_size);
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);
Expand All @@ -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 ? " ..." : "")
);
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2 changes: 1 addition & 1 deletion kernel/bpf/arraymap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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) {
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9 changes: 5 additions & 4 deletions kernel/bpf/hashtab.c
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Original file line number Diff line number Diff line change
Expand Up @@ -540,23 +540,24 @@ 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);

/* 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)),
Expand Down
20 changes: 12 additions & 8 deletions kernel/bpf/syscall.c
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Original file line number Diff line number Diff line change
Expand Up @@ -536,14 +536,18 @@ static int map_get_next_key(union bpf_attr *attr)
if (IS_ERR(map))
return PTR_ERR(map);

err = -ENOMEM;
key = kmalloc(map->key_size, GFP_USER);
if (!key)
goto err_put;

err = -EFAULT;
if (copy_from_user(key, ukey, map->key_size) != 0)
goto free_key;
if (ukey) {
err = -ENOMEM;
key = kmalloc(map->key_size, GFP_USER);
if (!key)
goto err_put;

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);
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29 changes: 25 additions & 4 deletions tools/testing/selftests/bpf/test_maps.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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),
Expand Down Expand Up @@ -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);

Expand All @@ -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);

Expand Down Expand Up @@ -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;

Expand Down Expand Up @@ -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;

Expand All @@ -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);

Expand Down Expand Up @@ -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 &&
Expand Down Expand Up @@ -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 &&
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
Expand All @@ -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);
}

Expand Down

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