Re: [dpdk-stable] [PATCH v3] ip_frag: recalculate data length of fragment

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi,
 
> In some situations, we would get several ip fragments, which total
> data length is less than minimum frame(64) and padding with zeros.
> Examples: Second Fragment "a0a1 a2a3 a4a5 a6a7 0000 0000 ..."
> and Third Fragment "a8a9 aaab acad aeaf b0b1 b2b3 ...".
> Finally, we would reassemble Second and Third Fragment like this
> "a0a1 a2a3 a4a5 a6a7 0000 0000 ... a8a9 aaab acad aeaf b0b1 ...",
> which is not correct!
> So, we need recalculate data length of fragment to remove padings!
> 
> Fixes: 7f0983ee331c ("ip_frag: check fragment length of incoming packet")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Yicai Lu <luyicai@huawei.com>
> ---
> v2 -> v3: Update the comments.
> ---
>  lib/librte_ip_frag/rte_ipv4_reassembly.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/librte_ip_frag/rte_ipv4_reassembly.c b/lib/librte_ip_frag/rte_ipv4_reassembly.c
> index 1dda8aca0..9a9fe3703 100644
> --- a/lib/librte_ip_frag/rte_ipv4_reassembly.c
> +++ b/lib/librte_ip_frag/rte_ipv4_reassembly.c
> @@ -117,6 +117,7 @@ rte_ipv4_frag_reassemble_packet(struct rte_ip_frag_tbl *tbl,
> 
>  	ip_ofs *= RTE_IPV4_HDR_OFFSET_UNITS;
>  	ip_len = rte_be_to_cpu_16(ip_hdr->total_length) - mb->l3_len;
> +	mb->data_len = ip_len + mb->l3_len + mb->l2_len;

That doesn't look correct.
Even one fragment can consist of multiple segments.
Plus you don't update mb->pkt_len.
To do it properly, you'll need something like:
trim = mb->pkt_len  - ip_len + mb->l3_len + mb->l2_len;
rte_pktmbuf_trim(mb, trim);

Though my preference would be to leave it as responsibility of the caller
(As it has to parse packet anyway to fill l2_len/l3_len and usually strips
l2 headers, etc).  

> 
>  	IP_FRAG_LOG(DEBUG, "%s:%d:\n"
>  		"mbuf: %p, tms: %" PRIu64
> --
> 2.28.0.windows.1