Re: [dpdk-dev] [PATCH v3 1/4] ip_frag: ensure minimum v4 fragmentation length

[Aaron Conole <aconole@redhat.com>]

"Ananyev, Konstantin" <konstantin.ananyev@intel.com> writes:

>> 
>> The IPv4 specification says that each fragment must at least the size of
>> an IP header plus 8 octets.  When attempting to run ipfrag using a
>> smaller size, the fragment library will return successful completion,
>> even though it is a violation of RFC791 (and updates).
>> 
>> Signed-off-by: Aaron Conole <aconole@redhat.com>
>> ---
>>  lib/librte_ip_frag/rte_ipv4_fragmentation.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/lib/librte_ip_frag/rte_ipv4_fragmentation.c b/lib/librte_ip_frag/rte_ipv4_fragmentation.c
>> index 9e9f986cc5..4baaf6355c 100644
>> --- a/lib/librte_ip_frag/rte_ipv4_fragmentation.c
>> +++ b/lib/librte_ip_frag/rte_ipv4_fragmentation.c
>> @@ -76,6 +76,12 @@ rte_ipv4_fragment_packet(struct rte_mbuf *pkt_in,
>>  	uint16_t fragment_offset, flag_offset, frag_size;
>>  	uint16_t frag_bytes_remaining;
>> 
>> +	/*
>> +	 * Ensure the IP fragmentation size is at least iphdr length + 8 octets
>> +	 */
>> +	if (unlikely(mtu_size < (sizeof(struct rte_ipv4_hdr) + 8*sizeof(char))))
>> +		return -EINVAL;
>> +
>
> Same comment as for ipv6: ipv4 min MTU is 68B.

I can change it.  I suspected that if I went with 68 here and 1280 in
the v6 code, I would get pushback, but I should have just submitted it
that way to begin.

> Why do we need extra checking here?

These are error conditions to submit to fragmentation module.  Someone
needs to do the check - either it is done in the application or the
library.  If the library doesn't, and the application writer doesn't
know they must write these checks (it isn't documented anywhere), then
we get non compliant behavior.  By putting it in the library, we can
clearly signal the application writer such a case has occurred.

Should we not do error checking?

>>  	/*
>>  	 * Ensure the IP payload length of all fragments is aligned to a
>>  	 * multiple of 8 bytes as per RFC791 section 2.3.
>> --
>> 2.25.1