netdev - Re: [PATCH bpf-next] bpf: deref map in BPF_PROG_BIND

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Date:   Fri, 2 Oct 2020 17:35:38 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next] bpf: deref map in BPF_PROG_BIND_MAP when it's
 already used

On Fri, Oct 2, 2020 at 5:26 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> We are missing a deref for the case when we are doing BPF_PROG_BIND_MAP
> on a map that's being already held by the program.
> There is 'if (ret) bpf_map_put(map)' below which doesn't trigger
> because we don't consider this an error.
> Let's add missing bpf_map_put() for this specific condition.
>
> Fixes: ef15314aa5de ("bpf: Add BPF_PROG_BIND_MAP syscall")
> Reported-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  kernel/bpf/syscall.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index f1528c2a6927..1110ecd7d1f3 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -4323,8 +4323,10 @@ static int bpf_prog_bind_map(union bpf_attr *attr)
>         used_maps_old = prog->aux->used_maps;
>
>         for (i = 0; i < prog->aux->used_map_cnt; i++)
> -               if (used_maps_old[i] == map)
> +               if (used_maps_old[i] == map) {
> +                       bpf_map_put(map);
>                         goto out_unlock;
> +               }
>
>         used_maps_new = kmalloc_array(prog->aux->used_map_cnt + 1,
>                                       sizeof(used_maps_new[0]),
> --
> 2.28.0.806.g8561365e88-goog
>