netdev - Re: [PATCH bpf] xdp: add NULL pointer check in __xdp

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Date:   Sat, 21 Jul 2018 21:56:05 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     daniel@...earbox.net, ast@...nel.org, bjorn.topel@...el.com,
        brouer@...hat.com, netdev@...r.kernel.org
Subject: Re: [PATCH bpf] xdp: add NULL pointer check in __xdp_return()

2018-07-21 2:18 GMT+09:00 Martin KaFai Lau <kafai@...com>:
> On Sat, Jul 21, 2018 at 01:04:45AM +0900, Taehee Yoo wrote:
>> rhashtable_lookup() can return NULL. so that NULL pointer
>> check routine should be added.
>>
>> Fixes: 02b55e5657c3 ("xdp: add MEM_TYPE_ZERO_COPY")
>> Signed-off-by: Taehee Yoo <ap420073@...il.com>
>> ---
>>  net/core/xdp.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/core/xdp.c b/net/core/xdp.c
>> index 9d1f220..1c12bc7 100644
>> --- a/net/core/xdp.c
>> +++ b/net/core/xdp.c
>> @@ -345,7 +345,8 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
>>               rcu_read_lock();
>>               /* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
>>               xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
>> -             xa->zc_alloc->free(xa->zc_alloc, handle);
>> +             if (xa)
>> +                     xa->zc_alloc->free(xa->zc_alloc, handle);
> hmm...It is not clear to me the "!xa" case don't have to be handled?

Thank you for reviewing!

Returning NULL pointer is bug case such as calling after use
xdp_rxq_info_unreg().
so that, I think it can't handle at that moment.
we can make __xdp_return to add WARN_ON_ONCE() or
add return error code to driver.
But I'm not sure if these is useful information.

I might have misunderstood scenario of MEM_TYPE_ZERO_COPY
because there is no use case of MEM_TYPE_ZERO_COPY yet.

Thanks!

>
>>               rcu_read_unlock();
>>       default:
>>               /* Not possible, checked in xdp_rxq_info_reg_mem_model() */
>> --
>> 2.9.3
>>