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Subject[PATCH 4.4 02/56] bpf: map_get_next_key to return first key on NULL
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Teng Qin <qinteng@fb.com>

commit 8fe45924387be6b5c1be59a7eb330790c61d5d10 upstream.

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>
Signed-off-by: Chenbo Feng <fengc@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/bpf/arraymap.c | 2 +-
kernel/bpf/hashtab.c | 9 +++++----
kernel/bpf/syscall.c | 18 +++++++++++-------
3 files changed, 17 insertions(+), 12 deletions(-)

--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -102,7 +102,7 @@ static void *array_map_lookup_elem(struc
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) {
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -169,12 +169,15 @@ static int htab_map_get_next_key(struct
struct hlist_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);
@@ -182,10 +185,8 @@ static int htab_map_get_next_key(struct
/* lookup the key */
l = lookup_elem_raw(head, hash, key, key_size);

- if (!l) {
- i = 0;
+ if (!l)
goto find_first_elem;
- }

/* key was found, get next key in the same bucket */
next_l = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(&l->hash_node)),
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -390,14 +390,18 @@ static int map_get_next_key(union bpf_at
if (IS_ERR(map))
return PTR_ERR(map);

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