Re: [PATCH bpf 1/2] libbpf: fix removal of inner map in bpf_object__create_map

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Martynas Pumputis <m@lambda.lt>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>
Subject: Re: [PATCH bpf 1/2] libbpf: fix removal of inner map in bpf_object__create_map
Date: Mon, 19 Jul 2021 15:58:30 -0700	[thread overview]
Message-ID: <CAEf4BzbjVdG57QuhvpxAuq8qz+T3+DbP28_CpF2Y4v1AmwkDKw@mail.gmail.com> (raw)
In-Reply-To: <20210719173838.423148-2-m@lambda.lt>

On Mon, Jul 19, 2021 at 10:36 AM Martynas Pumputis <m@lambda.lt> wrote:
>
> If creating an outer map of a BTF-defined map-in-map fails (via
> bpf_object__create_map()), then the previously created its inner map
> won't be destroyed.
>
> Fix this by ensuring that the destroy routines are not bypassed in the
> case of a failure.
>
> Fixes: 646f02ffdd49c ("libbpf: Add BTF-defined map-in-map support")
> Reported-by: Andrii Nakryiko <andrii@kernel.org>

Please preserve received acks between versions (unless some
significant changes happen between versions invalidating the original
ack):

Acked-by: John Fastabend <john.fastabend@gmail.com>

Thanks, applied (with few adjustments) to bpf-next, given we lived
with this bug for a long while and no one ever noticed/reported it
(and BPF map will be cleaned up when the process exits anyway).
Keeping it in bpf-next will make it easier for follow-up patches
changing/enhancing bpf_map__create_map() and will avoid merge
conflicts down the line.

> Signed-off-by: Martynas Pumputis <m@lambda.lt>
> ---
>  tools/lib/bpf/libbpf.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6f5e2757bb3c..dde521366579 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4479,6 +4479,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>  {
>         struct bpf_create_map_attr create_attr;
>         struct bpf_map_def *def = &map->def;
> +       int err = 0;
>
>         memset(&create_attr, 0, sizeof(create_attr));
>
> @@ -4521,8 +4522,6 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>
>         if (bpf_map_type__is_map_in_map(def->type)) {
>                 if (map->inner_map) {
> -                       int err;
> -
>                         err = bpf_object__create_map(obj, map->inner_map, true);
>                         if (err) {
>                                 pr_warn("map '%s': failed to create inner map: %d\n",
> @@ -4547,7 +4546,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>         if (map->fd < 0 && (create_attr.btf_key_type_id ||
>                             create_attr.btf_value_type_id)) {
>                 char *cp, errmsg[STRERR_BUFSIZE];
> -               int err = -errno;

needed empty line here

> +               err = -errno;
>
>                 cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
>                 pr_warn("Error in bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n",
> @@ -4560,8 +4559,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>                 map->fd = bpf_create_map_xattr(&create_attr);
>         }
>
> -       if (map->fd < 0)
> -               return -errno;
> +       err = map->fd < 0 ? -errno : 0;
>
>         if (bpf_map_type__is_map_in_map(def->type) && map->inner_map) {
>                 if (obj->gen_loader)
> @@ -4570,7 +4568,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>                 zfree(&map->inner_map);
>         }
>
> -       return 0;
> +       return err;
>  }
>
>  static int init_map_slots(struct bpf_object *obj, struct bpf_map *map)
> --
> 2.32.0
>