[dpdk-dev] [PATCH 3/4] net: introduce functions to verify L4 checksums

[Andrew Rybchenko]

On 4/30/21 6:42 PM, Ferruh Yigit wrote:
> On 4/27/2021 2:57 PM, Olivier Matz wrote:
>> Since commit d5df2ae0428a ("net: fix unneeded replacement of TCP
>> checksum 0"), the functions rte_ipv4_udptcp_cksum() and
>> rte_ipv6_udptcp_cksum() can return either 0x0000 or 0xffff when used to
>> verify a packet containing a valid checksum.
>>
>> Since these functions should be used to calculate the checksum to set in
>> a packet, introduce 2 new helpers for checksum verification. They return
>> 0 if the checksum is valid in the packet.
>>
>> Use this new helper in net/tap driver.
>>
>> Signed-off-by: Olivier Matz <olivier.matz at 6wind.com>
>> ---
>>  drivers/net/tap/rte_eth_tap.c |   7 +-
>>  lib/net/rte_ip.h              | 124 +++++++++++++++++++++++++++-------
>>  2 files changed, 104 insertions(+), 27 deletions(-)
>>
>> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
>> index 71282e8065..b14d5a1d55 100644
>> --- a/drivers/net/tap/rte_eth_tap.c
>> +++ b/drivers/net/tap/rte_eth_tap.c
>> @@ -365,11 +365,12 @@ tap_verify_csum(struct rte_mbuf *mbuf)
>>  					return;
>>  				}
>>  			}
>> -			cksum = rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
>> +			cksum_ok = !rte_ipv4_udptcp_cksum_verify(l3_hdr,
>> +								 l4_hdr);
>>  		} else { /* l3 == RTE_PTYPE_L3_IPV6, checked above */
>> -			cksum = rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
>> +			cksum_ok = !rte_ipv6_udptcp_cksum_verify(l3_hdr,
>> +								 l4_hdr);
>>  		}
>> -		cksum_ok = (cksum == 0) || (cksum == 0xffff);
>>  		mbuf->ol_flags |= cksum_ok ?
>>  			PKT_RX_L4_CKSUM_GOOD : PKT_RX_L4_CKSUM_BAD;
>>  	}
>> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
>> index 8c189009b0..ef84bcc5bf 100644
>> --- a/lib/net/rte_ip.h
>> +++ b/lib/net/rte_ip.h
>> @@ -344,20 +344,10 @@ rte_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
>>  }
>>  
>>  /**
>> - * Process the IPv4 UDP or TCP checksum.
>> - *
>> - * The IP and layer 4 checksum must be set to 0 in the packet by
>> - * the caller.
>> - *
>> - * @param ipv4_hdr
>> - *   The pointer to the contiguous IPv4 header.
>> - * @param l4_hdr
>> - *   The pointer to the beginning of the L4 header.
>> - * @return
>> - *   The complemented checksum to set in the IP packet.
>> + * @internal Calculate the non-complemented IPv4 L4 checksum
>>   */
>>  static inline uint16_t
>> -rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
>> +__rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
>>  {
>>  	uint32_t cksum;
>>  	uint32_t l3_len, l4_len;
>> @@ -374,16 +364,62 @@ rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
>>  	cksum += rte_ipv4_phdr_cksum(ipv4_hdr, 0);
>>  
>>  	cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
>> -	cksum = (~cksum) & 0xffff;
>> +
>> +	return (uint16_t)cksum;
>> +}
>> +
>> +/**
>> + * Process the IPv4 UDP or TCP checksum.
>> + *
>> + * The IP and layer 4 checksum must be set to 0 in the packet by
>> + * the caller.
>> + *
>> + * @param ipv4_hdr
>> + *   The pointer to the contiguous IPv4 header.
>> + * @param l4_hdr
>> + *   The pointer to the beginning of the L4 header.
>> + * @return
>> + *   The complemented checksum to set in the IP packet.
>> + */
>> +static inline uint16_t
>> +rte_ipv4_udptcp_cksum(const struct rte_ipv4_hdr *ipv4_hdr, const void *l4_hdr)
>> +{
>> +	uint16_t cksum = __rte_ipv4_udptcp_cksum(ipv4_hdr, l4_hdr);
>> +
>> +	cksum = ~cksum;
>> +
>>  	/*
>> -	 * Per RFC 768:If the computed checksum is zero for UDP,
>> +	 * Per RFC 768: If the computed checksum is zero for UDP,
>>  	 * it is transmitted as all ones
>>  	 * (the equivalent in one's complement arithmetic).
>>  	 */
>>  	if (cksum == 0 && ipv4_hdr->next_proto_id == IPPROTO_UDP)
>>  		cksum = 0xffff;
>>  
>> -	return (uint16_t)cksum;
>> +	return cksum;
>> +}
>> +
>> +/**
>> + * Validate the IPv4 UDP or TCP checksum.
>> + *
>> + * @param ipv4_hdr
>> + *   The pointer to the contiguous IPv4 header.
>> + * @param l4_hdr
>> + *   The pointer to the beginning of the L4 header.
>> + * @return
>> + *   Return 0 if the checksum is correct, else -1.
>> + */
>> +__rte_experimental
>> +static inline int
>> +rte_ipv4_udptcp_cksum_verify(const struct rte_ipv4_hdr *ipv4_hdr,
>> +			     const void *l4_hdr)
>> +{
>> +	uint16_t cksum = __rte_ipv4_udptcp_cksum(ipv4_hdr, l4_hdr);
>> +
>> +	if (cksum != 0xffff)
>> +		return -1;
>> +
>> +	return 0;
> 
> There is behavior change in tap verify, I am asking just to verify if expected,
> 
> Previously for UDP, if calculated checksum is '0', the 'rte_ipv4_udptcp_cksum()'
> returns 0xFFFF.
> And 0xFFFF is taken as good checksum by tap PMD.
> 
> With new 'rte_ipv4_udptcp_cksum_verify()', if calculated checksum is '0' it will
> be taken as bad checksum.
> 
> I don't know if calculated checksum with valid checksum in place can return 0.
> 
> 
> Also for TCP, 'rte_ipv4_udptcp_cksum_verify()' doesn't have inversion (cksum =
> ~cksum;) seems changing pass/fail status of the checksum, unless I am not
> missing anything here.

Yes, it looks suspicious to me as well.

Olivier, could you clarify, please.

>>  }
>>  
>>  /**
>> @@ -448,6 +484,25 @@ rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
>>  	return __rte_raw_cksum_reduce(sum);
>>  }
>>  
>> +/**
>> + * @internal Calculate the non-complemented IPv4 L4 checksum
>> + */
>> +static inline uint16_t
>> +__rte_ipv6_udptcp_cksum(const struct rte_ipv6_hdr *ipv6_hdr, const void *l4_hdr)
>> +{
>> +	uint32_t cksum;
>> +	uint32_t l4_len;
>> +
>> +	l4_len = rte_be_to_cpu_16(ipv6_hdr->payload_len);
>> +
>> +	cksum = rte_raw_cksum(l4_hdr, l4_len);
>> +	cksum += rte_ipv6_phdr_cksum(ipv6_hdr, 0);
>> +
>> +	cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
>> +
>> +	return (uint16_t)cksum;
>> +}
>> +
>>  /**
>>   * Process the IPv6 UDP or TCP checksum.
>>   *
>> @@ -464,16 +519,10 @@ rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
>>  static inline uint16_t
>>  rte_ipv6_udptcp_cksum(const struct rte_ipv6_hdr *ipv6_hdr, const void *l4_hdr)
>>  {
>> -	uint32_t cksum;
>> -	uint32_t l4_len;
>> -
>> -	l4_len = rte_be_to_cpu_16(ipv6_hdr->payload_len);
>> +	uint16_t cksum = __rte_ipv6_udptcp_cksum(ipv6_hdr, l4_hdr);
>>  
>> -	cksum = rte_raw_cksum(l4_hdr, l4_len);
>> -	cksum += rte_ipv6_phdr_cksum(ipv6_hdr, 0);
>> +	cksum = ~cksum;
>>  
>> -	cksum = ((cksum & 0xffff0000) >> 16) + (cksum & 0xffff);
>> -	cksum = (~cksum) & 0xffff;
>>  	/*
>>  	 * Per RFC 768: If the computed checksum is zero for UDP,
>>  	 * it is transmitted as all ones
>> @@ -482,7 +531,34 @@ rte_ipv6_udptcp_cksum(const struct rte_ipv6_hdr *ipv6_hdr, const void *l4_hdr)
>>  	if (cksum == 0 && ipv6_hdr->proto == IPPROTO_UDP)
>>  		cksum = 0xffff;
>>  
>> -	return (uint16_t)cksum;
>> +	return cksum;
>> +}
>> +
>> +/**
>> + * Validate the IPv6 UDP or TCP checksum.
>> + *
>> + * The function accepts a 0 checksum, since it can exceptionally happen. See 8.1
>> + * (Upper-Layer Checksums) in RFC 8200.
>> + *
>> + * @param ipv6_hdr
>> + *   The pointer to the contiguous IPv6 header.
>> + * @param l4_hdr
>> + *   The pointer to the beginning of the L4 header.
>> + * @return
>> + *   Return 0 if the checksum is correct, else -1.
>> + */
>> +__rte_experimental
>> +static inline int
>> +rte_ipv6_udptcp_cksum_verify(const struct rte_ipv6_hdr *ipv6_hdr,
>> +			     const void *l4_hdr)
>> +{
>> +	uint16_t cksum;
>> +
>> +	cksum = __rte_ipv6_udptcp_cksum(ipv6_hdr, l4_hdr);
>> +	if (cksum != 0xffff)
>> +		return -1;
>> +
>> +	return 0;
>>  }
> 
> Nitpicking but, 'rte_ipv4_udptcp_cksum_verify()' is almost same with this
> function ('rte_ipv6_udptcp_cksum_verify()') but they have different line
> spacing, can be good to have similar syntax for both.
>