Re: [PATCH 19/32] inany: Helper functions for handling addresses which could be IPv4 or IPv6

[Stefano Brivio <sbrivio@redhat.com>]

[Reviewed until 25/32 so far]

On Wed, 16 Nov 2022 15:41:59 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> struct tcp_conn stores an address which could be IPv6 or IPv4 using a
> union.  We can do this without an additional tag by encoding IPv4 addresses
> as IPv4-mapped IPv6 addresses.
> 
> This approach is useful wider than the specific place in tcp_conn, so
> expose a new 'union inany_addr' like this from a new inany.h.  Along with
> that create a number of helper functions to make working with these "inany"
> addresses easier.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  Makefile     |  6 ++--
>  inany.h      | 68 ++++++++++++++++++++++++++++++++++++++++
>  tcp.c        | 88 +++++++++++++++++++++++++---------------------------
>  tcp_conn.h   | 15 ++-------
>  tcp_splice.c |  1 +
>  5 files changed, 117 insertions(+), 61 deletions(-)
>  create mode 100644 inany.h
> 
> diff --git a/Makefile b/Makefile
> index 9046b0b..ca453aa 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -44,9 +44,9 @@ SRCS = $(PASST_SRCS) $(QRAP_SRCS)
>  MANPAGES = passt.1 pasta.1 qrap.1
>  
>  PASST_HEADERS = arch.h arp.h checksum.h conf.h dhcp.h dhcpv6.h icmp.h \
> -	isolation.h lineread.h log.h ndp.h netlink.h packet.h passt.h pasta.h \
> -	pcap.h port_fwd.h siphash.h tap.h tcp.h tcp_conn.h tcp_splice.h udp.h \
> -	util.h
> +	inany.h isolation.h lineread.h log.h ndp.h netlink.h packet.h passt.h \
> +	pasta.h pcap.h port_fwd.h siphash.h tap.h tcp.h tcp_conn.h \
> +	tcp_splice.h udp.h util.h
>  HEADERS = $(PASST_HEADERS) seccomp.h
>  
>  # On gcc 11 and 12, with -O2 and -flto, tcp_hash() and siphash_20b(), if
> diff --git a/inany.h b/inany.h
> new file mode 100644
> index 0000000..4e53da9
> --- /dev/null
> +++ b/inany.h
> @@ -0,0 +1,68 @@
> +/* SPDX-License-Identifier: AGPL-3.0-or-later
> + * Copyright Red Hat
> + * Author: David Gibson <david@gibson.dropbear.id.au>
> + *
> + * inany.h - Types and helpers for handling addresses which could be
> + *           IPv6 or IPv4 (encoded as IPv4-mapped IPv6 addresses)
> + */
> +
> +#include <assert.h>
> +
> +/** union inany_addr - Represents either an IPv4 or IPv6 address
> + * @a6:		Address as an IPv6 address, may be IPv4-mapped
> + * @_v4._zero:	All zero-bits for an IPv4 address
> + * @_v4._one:	All one-bits for an IPv4 address
> + * @_v4.a4:	If @a6 is an IPv4 mapped address, this is the raw IPv4 address
> + *
> + * Fields starting with _ shouldn't be accessed except via helpers.
> + */
> +union inany_addr {
> +	struct in6_addr a6;
> +	struct {
> +		uint8_t _zero[10];
> +		uint8_t _one[2];
> +		struct in_addr a4;
> +	} _v4mapped;

I'm not sure the extra _ are really worth it. I mean, that's not really
enforceable, so saying that v4mapped should only be accessed by helpers
should be equivalent.

> +};
> +
> +/** inany_v4 - Extract IPv4 address, if present, from IPv[46] address
> + * @addr:	IPv4 or IPv6 address
> + *
> + * Return: IPv4 address if @addr is IPv4, NULL otherwise
> + */
> +static inline const struct in_addr *inany_v4(const union inany_addr *addr)
> +{
> +	if (!IN6_IS_ADDR_V4MAPPED(&addr->a6))
> +		return NULL;
> +	return &addr->_v4mapped.a4;
> +}
> +
> +/** inany_equals - Compare two IPv[46] addresses
> + * @a, @b:	IPv[46] addresses
> + *
> + * Return: true if @a and @b are the same address
> + */
> +static inline bool inany_equals(const union inany_addr *a,
> +				const union inany_addr *b)
> +{
> +	return IN6_ARE_ADDR_EQUAL(&a->a6, &b->a6);
> +}
> +
> +/** inany_from_af - Set IPv[46] address from IPv4 or IPv6 address
> + * @aa:		Pointer to store IPv[46] address
> + * @af:		Address family of @addr
> + * @addr:	struct in_addr (IPv4) or struct in6_addr (IPv6)
> + */
> +static inline void inany_from_af(union inany_addr *aa, int af, const void *addr)
> +{
> +	if (af == AF_INET6) {
> +		aa->a6 = *((struct in6_addr *)addr);
> +	} else if (af == AF_INET) {
> +		memset(&aa->_v4mapped._zero, 0, sizeof(aa->_v4mapped._zero));
> +		memset(&aa->_v4mapped._one, 0xff, sizeof(aa->_v4mapped._one));
> +		aa->_v4mapped.a4 = *((struct in_addr *)addr);
> +	} else {
> +		/* Not valid to call with other address families */
> +		assert(0);
> +	}
> +}
> diff --git a/tcp.c b/tcp.c
> index 7686766..4040198 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -301,6 +301,7 @@
>  #include "conf.h"
>  #include "tcp_splice.h"
>  #include "log.h"
> +#include "inany.h"
>  
>  #include "tcp_conn.h"
>  
> @@ -404,7 +405,7 @@ struct tcp6_l2_head {	/* For MSS6 macro: keep in sync with tcp6_l2_buf_t */
>  #define OPT_SACK	5
>  #define OPT_TS		8
>  
> -#define CONN_V4(conn)		IN6_IS_ADDR_V4MAPPED(&conn->a.a6)
> +#define CONN_V4(conn)		(!!inany_v4(&(conn)->addr))
>  #define CONN_V6(conn)		(!CONN_V4(conn))
>  #define CONN_IS_CLOSING(conn)						\
>  	((conn->events & ESTABLISHED) &&				\
> @@ -438,7 +439,7 @@ static int tcp_sock_init_ext	[NUM_PORTS][IP_VERSIONS];
>  static int tcp_sock_ns		[NUM_PORTS][IP_VERSIONS];
>  
>  /* Table of destinations with very low RTT (assumed to be local), LRU */
> -static struct in6_addr low_rtt_dst[LOW_RTT_TABLE_SIZE];
> +static union inany_addr low_rtt_dst[LOW_RTT_TABLE_SIZE];
>  
>  /* Static buffers */
>  
> @@ -861,7 +862,7 @@ static int tcp_rtt_dst_low(const struct tcp_tap_conn *conn)
>  	int i;
>  
>  	for (i = 0; i < LOW_RTT_TABLE_SIZE; i++)
> -		if (IN6_ARE_ADDR_EQUAL(&conn->a.a6, low_rtt_dst + i))
> +		if (inany_equals(&conn->addr, low_rtt_dst + i))
>  			return 1;
>  
>  	return 0;
> @@ -883,7 +884,7 @@ static void tcp_rtt_dst_check(const struct tcp_tap_conn *conn,
>  		return;
>  
>  	for (i = 0; i < LOW_RTT_TABLE_SIZE; i++) {
> -		if (IN6_ARE_ADDR_EQUAL(&conn->a.a6, low_rtt_dst + i))
> +		if (inany_equals(&conn->addr, low_rtt_dst + i))
>  			return;
>  		if (hole == -1 && IN6_IS_ADDR_UNSPECIFIED(low_rtt_dst + i))
>  			hole = i;
> @@ -895,10 +896,10 @@ static void tcp_rtt_dst_check(const struct tcp_tap_conn *conn,
>  	if (hole == -1)
>  		return;
>  
> -	memcpy(low_rtt_dst + hole++, &conn->a.a6, sizeof(conn->a.a6));
> +	low_rtt_dst[hole++] = conn->addr;
>  	if (hole == LOW_RTT_TABLE_SIZE)
>  		hole = 0;
> -	memcpy(low_rtt_dst + hole, &in6addr_any, sizeof(conn->a.a6));
> +	inany_from_af(low_rtt_dst + hole, AF_INET6, &in6addr_any);
>  #else
>  	(void)conn;
>  	(void)tinfo;
> @@ -1187,13 +1188,14 @@ static int tcp_hash_match(const struct tcp_tap_conn *conn,
>  			  int af, const void *addr,
>  			  in_port_t tap_port, in_port_t sock_port)
>  {
> -	if (af == AF_INET && CONN_V4(conn)			&&
> -	    !memcmp(&conn->a.a4.a, addr, sizeof(conn->a.a4.a))	&&
> +	const struct in_addr *a4 = inany_v4(&conn->addr);
> +
> +	if (af == AF_INET && a4	&& !memcmp(a4, addr, sizeof(*a4)) &&
>  	    conn->tap_port == tap_port && conn->sock_port == sock_port)
>  		return 1;
>  
>  	if (af == AF_INET6					&&
> -	    IN6_ARE_ADDR_EQUAL(&conn->a.a6, addr)		&&
> +	    IN6_ARE_ADDR_EQUAL(&conn->addr.a6, addr)		&&
>  	    conn->tap_port == tap_port && conn->sock_port == sock_port)
>  		return 1;

Note to self or other reviewers: switch to inany_equals() in 22/32.

-- 
Stefano