[bpf-next,v2,2/7] bpf/syscall: allow key to be null in map functions

This commit adds the required logic to allow key being NULL
in case the key_size of the map is 0.

A new __bpf_copy_key function helper only copies the key from
userpsace when key_size != 0, otherwise it enforces that key must be
null.

Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>
---
 kernel/bpf/syscall.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

On Wed, Oct 10, 2018 at 7:06 AM Mauricio Vasquez B
<mauricio.vasquez@polito.it> wrote:
>
> This commit adds the required logic to allow key being NULL
> in case the key_size of the map is 0.
>
> A new __bpf_copy_key function helper only copies the key from
> userpsace when key_size != 0, otherwise it enforces that key must be
> null.
>
> Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>
Acked-by: Song Liu <songliubraving@fb.com>
> ---
>  kernel/bpf/syscall.c |   19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 4f416234251f..f36c080ad356 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -651,6 +651,17 @@ int __weak bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
>         return -ENOTSUPP;
>  }
>
> +static void *__bpf_copy_key(void __user *ukey, u64 key_size)
> +{
> +       if (key_size)
> +               return memdup_user(ukey, key_size);
> +
> +       if (ukey)
> +               return ERR_PTR(-EINVAL);
> +
> +       return NULL;
> +}
> +
>  /* last field in 'union bpf_attr' used by this command */
>  #define BPF_MAP_LOOKUP_ELEM_LAST_FIELD value
>
> @@ -678,7 +689,7 @@ static int map_lookup_elem(union bpf_attr *attr)
>                 goto err_put;
>         }
>
> -       key = memdup_user(ukey, map->key_size);
> +       key = __bpf_copy_key(ukey, map->key_size);
>         if (IS_ERR(key)) {
>                 err = PTR_ERR(key);
>                 goto err_put;
> @@ -774,7 +785,7 @@ static int map_update_elem(union bpf_attr *attr)
>                 goto err_put;
>         }
>
> -       key = memdup_user(ukey, map->key_size);
> +       key = __bpf_copy_key(ukey, map->key_size);
>         if (IS_ERR(key)) {
>                 err = PTR_ERR(key);
>                 goto err_put;
> @@ -876,7 +887,7 @@ static int map_delete_elem(union bpf_attr *attr)
>                 goto err_put;
>         }
>
> -       key = memdup_user(ukey, map->key_size);
> +       key = __bpf_copy_key(ukey, map->key_size);
>         if (IS_ERR(key)) {
>                 err = PTR_ERR(key);
>                 goto err_put;
> @@ -928,7 +939,7 @@ static int map_get_next_key(union bpf_attr *attr)
>         }
>
>         if (ukey) {
> -               key = memdup_user(ukey, map->key_size);
> +               key = __bpf_copy_key(ukey, map->key_size);
>                 if (IS_ERR(key)) {
>                         err = PTR_ERR(key);
>                         goto err_put;
>