[PATCH 4.4 02/56] bpf: map_get_next_key to return first key on NULL

[Greg Kroah-Hartman]

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

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

From: Teng Qin <qint...@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 <qint...@fb.com>
Signed-off-by: Alexei Starovoitov <a...@kernel.org>
Acked-by: Daniel Borkmann <dan...@iogearbox.net>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Chenbo Feng <fe...@google.com>
Cc: Lorenzo Colitti <lore...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@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);