From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: Re: [RFC bpf-next 2/4] bpf: return EOPNOTSUPP when map lookup isn't
 supported
Date: Wed, 19 Sep 2018 08:14:24 -0700
Message-ID: <20180919151422.tysdcku2hxaq37xw@ast-mbp>
References: <20180919075143.9308-1-bhole_prashant_q7@lab.ntt.co.jp>
 <20180919075143.9308-3-bhole_prashant_q7@lab.ntt.co.jp>
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Cc: Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Quentin Monnet <quentin.monnet@netronome.com>,
        "David S . Miller" <davem@davemloft.net>, netdev@vger.kernel.org
To: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
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On Wed, Sep 19, 2018 at 04:51:41PM +0900, Prashant Bhole wrote:
> Return ERR_PTR(-EOPNOTSUPP) from map_lookup_elem() methods of below
> map types:
> - BPF_MAP_TYPE_PROG_ARRAY
> - BPF_MAP_TYPE_STACK_TRACE
> - BPF_MAP_TYPE_XSKMAP
> - BPF_MAP_TYPE_SOCKMAP/BPF_MAP_TYPE_SOCKHASH
> 
> Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
> ---
>  kernel/bpf/arraymap.c | 2 +-
>  kernel/bpf/sockmap.c  | 2 +-
>  kernel/bpf/stackmap.c | 2 +-
>  kernel/bpf/xskmap.c   | 2 +-
>  4 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index dded84cbe814..24583da9ffd1 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -449,7 +449,7 @@ static void fd_array_map_free(struct bpf_map *map)
>  
>  static void *fd_array_map_lookup_elem(struct bpf_map *map, void *key)
>  {
> -	return NULL;
> +	return ERR_PTR(-EOPNOTSUPP);
>  }

conceptually the set looks good to me.
Please add a test to test_verifier.c to make sure
that these lookup helpers cannot be called from BPF program.
Otherwise this diff may cause crashes.