linux-kernel - Re: [PATCH bpf-next] bpf: prevent leak of lsm program after failed attach

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Date:   Tue, 13 Dec 2022 10:43:34 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Milan Landaverde <milan@...verde.com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: prevent leak of lsm program after failed attach

On Tue, Dec 13, 2022 at 9:58 AM Milan Landaverde <milan@...verde.com> wrote:
>
> In [0], we added the ability to bpf_prog_attach LSM programs to cgroups,
> but in our validation to make sure the prog is meant to be attached to
> BPF_LSM_CGROUP, we return too early if the check fails. This results in
> lack of decrementing prog's refcnt (through bpf_prog_put)
> leaving the LSM program alive past the point of the expected lifecycle.
> This fix allows for the decrement to take place.
>
> [0] https://lore.kernel.org/all/20220628174314.1216643-4-sdf@google.com/
>
> Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
> Signed-off-by: Milan Landaverde <milan@...verde.com>

Makes sense, thank you!

Reviewed-by: Stanislav Fomichev <sdf@...gle.com>

> ---
>  kernel/bpf/syscall.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 35972afb6850..64131f88c553 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3518,9 +3518,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
>         case BPF_PROG_TYPE_LSM:
>                 if (ptype == BPF_PROG_TYPE_LSM &&
>                     prog->expected_attach_type != BPF_LSM_CGROUP)
> -                       return -EINVAL;
> -
> -               ret = cgroup_bpf_prog_attach(attr, ptype, prog);
> +                       ret = -EINVAL;
> +               else
> +                       ret = cgroup_bpf_prog_attach(attr, ptype, prog);
>                 break;
>         default:
>                 ret = -EINVAL;
> --
> 2.34.1
>