Re: [PATCH bpf-next v3 1/7] bpf: Refactor trampoline update code

[Daniel Borkmann]

On 3/4/20 4:47 PM, KP Singh wrote:
> From: KP Singh <kpsingh@xxxxxxxxxx>
>
> As we need to introduce a third type of attachment for trampolines, the
> flattened signature of arch_prepare_bpf_trampoline gets even more
> complicated.
>
> Refactor the prog and count argument to arch_prepare_bpf_trampoline to
> use bpf_tramp_progs to simplify the addition and accounting for new
> attachment types.
>
> Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>
> Acked-by: Andrii Nakryiko <andriin@xxxxxx>

[...]
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index c498f0fffb40..9f7e0328a644 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -320,6 +320,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>   	struct bpf_struct_ops_value *uvalue, *kvalue;
>   	const struct btf_member *member;
>   	const struct btf_type *t = st_ops->type;
> +	struct bpf_tramp_progs *tprogs = NULL;
>   	void *udata, *kdata;
>   	int prog_fd, err = 0;
>   	void *image;
> @@ -425,10 +426,18 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>   			goto reset_unlock;
>   		}
>   
> +		tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
> +		if (!tprogs) {
> +			err = -ENOMEM;
> +			goto reset_unlock;
> +		}
> +

Looking over the code again, I'm quite certain that here's a memleak
since the kcalloc() is done in the for_each_member() loop in the ops
update but then going out of scope and in the exit path we only kfree
the last tprogs.

> +		tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
> +		tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
>   		err = arch_prepare_bpf_trampoline(image,
>   						  st_map->image + PAGE_SIZE,
>   						  &st_ops->func_models[i], 0,
> -						  &prog, 1, NULL, 0, NULL);
> +						  tprogs, NULL);
>   		if (err < 0)
>   			goto reset_unlock;
>   
> @@ -469,6 +478,7 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
>   	memset(uvalue, 0, map->value_size);
>   	memset(kvalue, 0, map->value_size);
>   unlock:
> +	kfree(tprogs);
>   	mutex_unlock(&st_map->lock);
>   	return err;
>   }