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

[Stanislav Fomichev <sdf@google.com>]

On Tue, Dec 13, 2022 at 9:58 AM Milan Landaverde <milan@mdaverde.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@mdaverde.com>

Makes sense, thank you!

Reviewed-by: Stanislav Fomichev <sdf@google.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
>