Re: [PATCH 04/14] Add csum_udp4() helper for calculating UDP over IPv4 checksums

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Oct 18, 2022 at 05:03:09AM +0200, Stefano Brivio wrote:
11;rgb:ffff/ffff/ffff> On Mon, 17 Oct 2022 19:57:57 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > At least two places in passt fill in UDP over IPv4 checksums, although
> > since UDP checksums are optional with IPv4 that just amounts to storing
> > a 0 (in tap_ip_send()) or leaving a 0 from an earlier initialization (in
> > dhcp()).  For consistency, add a helper for this "calculation".
> > 
> > Just for the heck of it, add the option (compile time disabled for now) to
> > calculate real UDP checksums.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  checksum.c | 33 +++++++++++++++++++++++++++++++++
> >  checksum.h |  3 +++
> >  dhcp.c     |  2 +-
> >  tap.c      |  2 +-
> >  4 files changed, 38 insertions(+), 2 deletions(-)
> > 
> > diff --git a/checksum.c b/checksum.c
> > index 0849fb1..72f1cfb 100644
> > --- a/checksum.c
> > +++ b/checksum.c
> > @@ -56,6 +56,11 @@
> >  #include <linux/icmp.h>
> >  #include <linux/icmpv6.h>
> >  
> > +/* Checksums are optional for UDP over IPv4, so we usually just set
> > + * them to 0.  Change this 1 to calculate real UDP over IPv4 checksums
> 
> to 1

Done.

> > + */
> > +#define UDP4_REAL_CHECKSUMS	0
> > +
> >  /**
> >   * sum_16b() - Calculate sum of 16-bit words
> >   * @buf:	Input buffer
> > @@ -109,6 +114,34 @@ uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init)
> >  	return (uint16_t)~csum_fold(sum_16b(buf, len) + init);
> >  }
> >  
> > +/**
> > + * csum_udp4() - Calculate checksum for a UDP over IPv4 packet
> 
> and set

Done.

> > + * @udp4hr:	UDP header, initialized apart from checksum
> > + * @saddr:	IPv4 source address
> > + * @daddr:	IPv4 destination address
> > + * @payload:	ICMPv4 packet payload
> > + * @len:	Length of @payload (not including UDP)
> > + */
> > +void csum_udp4(struct udphdr *udp4hr,
> > +	       in_addr_t saddr, in_addr_t daddr,
> > +	       const void *payload, size_t len)
> > +{
> > +	/* UDP checksums are optional, so don't bother */
> > +	udp4hr->check = 0;
> > +
> > +	if (UDP4_REAL_CHECKSUMS) {
> > +		/* UNTESTED: if we did want real UDPv4 checksums, this
> > +		 * is roughly what we'd need */
> > +		uint32_t psum = csum_fold(htonl(saddr))
> > +			+ csum_fold(htonl(daddr))
> > +			+ htons(len + sizeof(*udp4hr))
> > +			+ htons(IPPROTO_UDP);
> > +		/* Add in partial checksum for the UDP header alone */
> > +		psum += sum_16b(udp4hr, sizeof(*udp4hr));
> > +		udp4hr->check = csum_unaligned(payload, len, psum);
> > +	}
> > +}
> > +
> >  /**
> >   * csum_icmp4() - Calculate checksum for an ICMPv4 packet
> >   * @icmp4hr:	ICMPv4 header, initialized apart from checksum
> > diff --git a/checksum.h b/checksum.h
> > index 1b9f48e..a9502b9 100644
> > --- a/checksum.h
> > +++ b/checksum.h
> > @@ -13,6 +13,9 @@ struct icmp6hdr;
> >  uint32_t sum_16b(const void *buf, size_t len);
> >  uint16_t csum_fold(uint32_t sum);
> >  uint16_t csum_unaligned(const void *buf, size_t len, uint32_t init);
> > +void csum_udp4(struct udphdr *udp4hr,
> > +	       in_addr_t saddr, in_addr_t daddr,
> > +	       const void *payload, size_t len);
> 
> Horizontal space.

Done.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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