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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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);