Re: [PATCH] net: convert sk_filter.refcnt from atomic_t to refcount_t

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello!

On 3/18/2017 3:58 PM, Elena Reshetova wrote:

> refcount_t type and corresponding API should be
> used instead of atomic_t when the variable is used as
> a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free
> situations.
>
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: David Windsor <dwindsor@gmail.com>
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index ebaeaf2..62267e2 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
[...]
> @@ -1179,12 +1179,13 @@ static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk)
>  		return -ENOMEM;
>
>  	fp->prog = prog;
> -	atomic_set(&fp->refcnt, 0);
> +	refcount_set(&fp->refcnt, 1);
>
>  	if (!sk_filter_charge(sk, fp)) {
>  		kfree(fp);
>  		return -ENOMEM;
>  	}
> +	refcount_set(&fp->refcnt, 1);

    Why do it twice?

[...]

MBR, Sergei