netdev - Re: [RFC bpf-next 2/4] bpf: return EOPNOTSUPP when map lookup isn't supported

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Date:   Wed, 19 Sep 2018 13:40:26 -0500
From:   Mauricio Vasquez <mauricio.vasquez@...ito.it>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC bpf-next 2/4] bpf: return EOPNOTSUPP when map lookup isn't
 supported



On 09/19/2018 10:14 AM, Alexei Starovoitov wrote:
> 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@....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.
>
>
I think we can remove all these stub functions that return EOPNOTSUPP or 
EINVAL and return the error in syscall.c if ops->map_[update, delete, 
lookup, ...] is null.
This will require to extend (and test) the verifier to guarantee that 
those helpers are not called in wrong maps, for example 
map_delete_element in array like maps.

Would it make sense?