[dpdk-dev] [PATCH] lib/librte_net: fix bug for ipv4 checksumcalculating

[Morten Brørup]

> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of guohongzhi (A)
> Sent: Friday, May 15, 2020 3:05 AM
> 
> Ok, later I will write a patch to solve the problem of tcpdump checksum
> 
> -----Original Message-----
> From: Morten Brørup [mailto:mb at smartsharesystems.com]
> Sent: Thursday,May 14,2020 20:57
> To: guohongzhi (A) <guohongzhi1 at huawei.com>; dev at dpdk.org
> Cc: olivier.matz at 6wind.com; konstantin.ananyev at intel.com;
> jiayu.hu at intel.com; ferruh.yigit at intel.com; nicolas.chautru at intel.com;
> cristian.dumitrescu at intel.com; Zhoujingbin (Robin, Russell Lab)
> <zhoujingbin at huawei.com>; chenchanghu <chenchanghu at huawei.com>; Lilijun
> (Jerry) <jerry.lilijun at huawei.com>; Linhaifeng <haifeng.lin at huawei.com>
> Subject: RE: [dpdk-dev] [PATCH] lib/librte_net: fix bug for ipv4
> checksumcalculating
> 
> > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of guohongzhi
> > Sent: Thursday, May 14, 2020 3:27 AM
> >
> > The function of rte_ipv4_cksum for calculating the checksum of IPv4
> > header is incorrect.
> > This function will return checksum value like 0xffff.
> > This value, however, is considered an illegal checksum on some
> > switches(like Trident3).
> >
> > RFC 1624 specifies the IPv4 checksum as follows:
> > https://tools.ietf.org/rfc/rfc1624
> > Since there is guaranteed to be at least one
> >    non-zero field in the IP header, and the checksum field in the
> >    protocol header is the complement of the sum, the checksum field
> can
> >    never contain ~(+0), which is -0 (0xFFFF).  It can, however,
> contain
> >    ~(-0), which is +0 (0x0000).
> >
> > ---
> >  lib/librte_net/rte_ip.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h index
> > 1ceb7b7..ece2e43 100644
> > --- a/lib/librte_net/rte_ip.h
> > +++ b/lib/librte_net/rte_ip.h
> > @@ -267,7 +267,7 @@ rte_ipv4_cksum(const struct rte_ipv4_hdr
> > *ipv4_hdr)  {
> >  	uint16_t cksum;
> >  	cksum = rte_raw_cksum(ipv4_hdr, sizeof(struct rte_ipv4_hdr));
> > -	return (cksum == 0xffff) ? cksum : (uint16_t)~cksum;
> > +	return (uint16_t)~cksum;
> >  }
> >
> >  /**
> > --
> > 2.21.0.windows.1
> >
> >
> 
> Well spotted!
> 
> Reviewed-By: Morten Brørup <mb at smartsharesystems.com>
> 

While you are at it, you could also fix a Big Endian bug in __rte_raw_cksum():

	/* if length is in odd bytes */
	if (len == 1)
+#if RTE_BYTE_ORDER == RTE_BIG_ENDIAN
+		sum += *((const uint8_t *)u16_buf) << 8;
+#else
		sum += *((const uint8_t *)u16_buf);
+#endif

	return sum;

> 
> Would you consider writing another patch splitting
> rte_ipv4_udptcp_cksum() up into rte_ipv4_udp_cksum() and
> rte_ipv4_tcp_cksum(), so the TCP checksum will be calculated correctly?
> 
> RFC 768 for UDP specifies:
> 
> If the computed  checksum  is zero,  it is transmitted  as all ones
> (the equivalent  in one's complement  arithmetic).   An all zero
> transmitted checksum  value means that the transmitter  generated  no
> checksum  (for debugging or for higher level protocols that don't
> care).
> 
> RFC 793 for TCP has no such special treatment for the checksum of zero,
> but rte_ipv4_udptcp_cksum() implements the UDP special treatment
> anyway.