Re: [PATCH v2 09/12] icmp: Consolidate icmp_sock_handler() with icmpv6_sock_handler()

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

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On Sat, Jan 06, 2024 at 05:00:44PM +0100, Stefano Brivio wrote:
> On Thu, 21 Dec 2023 17:53:24 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > Currently we have separate handlers for ICMP and ICMPv6 ping replies.
> > Although there are a number of points of difference, with some creative
> > refactoring we can combine these together sensibly.  Although it doesn't
> > save a vast amount of code, it does make it clearer that we're performing
> > basically the same steps for each case.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  icmp.c  | 90 ++++++++++++++++++++++-----------------------------------
> >  icmp.h  |  3 +-
> >  passt.c |  4 +--
> >  3 files changed, 37 insertions(+), 60 deletions(-)
> > 
> > diff --git a/icmp.c b/icmp.c
> > index f6c744a..b26c61f 100644
> > --- a/icmp.c
> > +++ b/icmp.c
> > @@ -57,85 +57,63 @@ struct icmp_id_sock {
> >  static struct icmp_id_sock icmp_id_map[IP_VERSIONS][ICMP_NUM_IDS];
> >  
> >  /**
> > - * icmp_sock_handler() - Handle new data from IPv4 ICMP socket
> > + * icmp_sock_handler() - Handle new data from ICMP or ICMPv6 socket
> >   * @c:		Execution context
> > + * @af:		Address family (AF_INET or AF_INET6)
> >   * @ref:	epoll reference
> >   */
> > -void icmp_sock_handler(const struct ctx *c, union epoll_ref ref)
> > +void icmp_sock_handler(const struct ctx *c, int af, union epoll_ref ref)
> >  {
> > +	struct icmp_id_sock *const id_map = af == AF_INET
> > +		? &icmp_id_map[V4][ref.icmp.id] : &icmp_id_map[V6][ref.icmp.id];
> > +	const char *const pname = af == AF_INET ? "ICMP" : "ICMPv6";
> >  	char buf[USHRT_MAX];
> > -	struct icmphdr *ih = (struct icmphdr *)buf;
> > -	struct sockaddr_in sr;
> > +	union {
> > +		struct sockaddr sa;
> > +		struct sockaddr_in sa4;
> > +		struct sockaddr_in6 sa6;
> > +	} sr;
> >  	socklen_t sl = sizeof(sr);
> > -	uint16_t seq, id;
> > +	uint16_t seq;
> >  	ssize_t n;
> >  
> >  	if (c->no_icmp)
> >  		return;
> >  
> > -	n = recvfrom(ref.fd, buf, sizeof(buf), 0, (struct sockaddr *)&sr, &sl);
> > +	n = recvfrom(ref.fd, buf, sizeof(buf), 0, &sr.sa, &sl);
> >  	if (n < 0)
> >  		return;
> >  
> > -	seq = ntohs(ih->un.echo.sequence);
> > -
> > -	/* Adjust the packet to have the ID the guest was using, rather than the
> > -	 * host chosen value */
> > -	id = ref.icmp.id;
> > -	ih->un.echo.id = htons(id);
> > +	if (af == AF_INET) {
> > +		struct icmphdr *ih4 = (struct icmphdr *)buf;
> >  
> > -	if (c->mode == MODE_PASTA) {
> > -		if (icmp_id_map[V4][id].seq == seq)
> > -			return;
> > +		/* Adjust packet back to guest-side ID */
> > +		ih4->un.echo.id = htons(ref.icmp.id);
> > +		seq = ntohs(ih4->un.echo.sequence);
> > +	} else if (af == AF_INET6) {
> > +		struct icmp6hdr *ih6 = (struct icmp6hdr *)buf;
> >  
> > -		icmp_id_map[V4][id].seq = seq;
> > +		/* Adjust packet back to guest-side ID */
> > +		ih6->icmp6_identifier = htons(ref.icmp.id);
> > +		seq = ntohs(ih6->icmp6_sequence);
> > +	} else {
> > +		ASSERT(0);
> >  	}
> >  
> > -	debug("ICMP: echo reply to tap, ID: %i, seq: %i", id, seq);
> > -
> > -	tap_icmp4_send(c, sr.sin_addr, tap_ip4_daddr(c), buf, n);
> > -}
> > -
> > -/**
> > - * icmpv6_sock_handler() - Handle new data from ICMPv6 socket
> > - * @c:		Execution context
> > - * @ref:	epoll reference
> > - */
> > -void icmpv6_sock_handler(const struct ctx *c, union epoll_ref ref)
> > -{
> > -	char buf[USHRT_MAX];
> > -	struct icmp6hdr *ih = (struct icmp6hdr *)buf;
> > -	struct sockaddr_in6 sr;
> > -	socklen_t sl = sizeof(sr);
> > -	uint16_t seq, id;
> > -	ssize_t n;
> > -
> > -	if (c->no_icmp)
> > -		return;
> > -
> > -	n = recvfrom(ref.fd, buf, sizeof(buf), 0, (struct sockaddr *)&sr, &sl);
> > -	if (n < 0)
> > -		return;
> > -
> > -	seq = ntohs(ih->icmp6_sequence);
> > -
> > -	/* Adjust the packet to have the ID the guest was using, rather than the
> > -	 * host chosen value */
> > -	id = ref.icmp.id;
> > -	ih->icmp6_identifier = htons(id);
> > -
> > -	/* In PASTA mode, we'll get any reply we send, discard them. */
> >  	if (c->mode == MODE_PASTA) {
> 
> The comment here should be kept -- the kernel behaviour was rather
> surprising to me, and I would have otherwise no idea why we return
> early here.

Good point, comment restored.

-- 
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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