Re: [dpdk-dev] [PATCH] net: check that seg is valid before dereference

[Chas Williams <3chas3@gmail.com>]

On 9/28/20 11:01 PM, wangyunjian wrote:
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Chas Williams
>> Sent: Monday, September 28, 2020 11:32 PM
>> To: dev@dpdk.org
>> Cc: olivier.matz@6wind.com; Chas Williams <3chas3@gmail.com>
>> Subject: [dpdk-dev] [PATCH] net: check that seg is valid before dereference
>>
>> If the overall pkt_len and segment lengths are out of agreement, it is possible
>> for the seg to be NULL after the loop. Add assert to check this condition in
>> debug builds.
>>
>> Fixes: c442fed81bb9 ("net: add function to calculate checksum in mbuf")
>>
>> Signed-off-by: Chas Williams <3chas3@gmail.com>
>> ---
>>   lib/librte_net/rte_ip.h | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h index
>> fcd1eb342..6b3e4cdda 100644
>> --- a/lib/librte_net/rte_ip.h
>> +++ b/lib/librte_net/rte_ip.h
>> @@ -225,6 +225,7 @@ rte_raw_cksum_mbuf(const struct rte_mbuf *m,
>> uint32_t off, uint32_t len,
>>                      break;
>>              off -= seglen;
>>      }
>> +    RTE_ASSERT(seg != NULL);
>
> Is it better to return an error code?

Maybe. However, to get into this state your mbuf chain is already badly broken.
Personally, I would prefer an immediate failure in the application so
I can track
down the source of this error.

No one is checking the return code now, so returning one wouldn't
really help unless I also fix the callers. Lastly, would everyone
be happy with an extra branch in the virtio RX path?


>
>>      seglen -= off;
>>      buf = rte_pktmbuf_mtod_offset(seg, const char *, off);
>>      if (seglen >= len) {
>> --
>> 2.26.2
>