Re: [PATCH v3 04/11] fwd: Check all configured addresses in guest accessibility functions

[Jon Maloy <jmaloy@redhat.com>]

On 2026-02-04 08:16, David Gibson wrote:
> On Fri, Jan 30, 2026 at 04:44:40PM -0500, Jon Maloy wrote:
>> As a preparation for handling multiple addresses, we update
>> fwd_guest_accessible4() and fwd_guest_accessible6() to check
>> against all addresses in the unified addrs[] array using the
>> for_each_addr() macro.
>>
>> This ensures that when multiple addresses are configured via -a options,
>> inbound traffic for any of them is correctly detected as having no valid
>> forwarding path, and subsequently dropped. This occurs when a peer
>> address collides with an address the guest is using, and we have no
>> translation for it.
>>
>> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
>>
>> ---
>> v2: Updated commit log to make it clearer
>> v3: Adapted to changes earlier in the series
>> ---
>>   fwd.c | 25 +++++++++++++++++--------
>>   1 file changed, 17 insertions(+), 8 deletions(-)
>>
>> diff --git a/fwd.c b/fwd.c
>> index 54248a3..20d581d 100644
>> --- a/fwd.c
>> +++ b/fwd.c
>> @@ -502,6 +502,8 @@ static bool is_dns_flow(uint8_t proto, const struct flowside *ini)
>>   static bool fwd_guest_accessible4(const struct ctx *c,
>>   				    const struct in_addr *addr)
> 
> With the changes to this point, there's no longer a point to having
> separate fwd_guest_accessible4() and fwd_guest_accessible6()
> functions.  fwd_guest_accessible() can check against the combined list
> in a single pass.

Absolutely. I have already identified several functions which can be
unified in a similar way, and have already implemented some.
But I still want to wait with such changes until this series has been
applied.

///jon


> 
> This is an example of the simplfications that I think will outweigh
> the complications introduced by using merged list for v4 and v6
> addresses.
> 
>>   {
>> +	const struct inany_addr_entry *e;
>> +
>>   	if (IN4_IS_ADDR_LOOPBACK(addr))
>>   		return false;
>>   
>> @@ -513,12 +515,15 @@ static bool fwd_guest_accessible4(const struct ctx *c,
>>   	if (IN4_IS_ADDR_UNSPECIFIED(addr))
>>   		return false;
>>   
>> -	/* For IPv4, addr_seen is initialised to addr, so is always a valid
>> -	 * address
>> +	/* Check against all configured guest addresses */
>> +	for_each_addr(c, e, AF_INET)
>> +		if (IN4_ARE_ADDR_EQUAL(addr, inany_v4(&e->addr)))
>> +			return false;
>> +
>> +	/* Also check addr_seen: it tracks the address the guest is actually
>> +	 * using, which may differ from configured addresses.
>>   	 */
>> -	if ((first_v4(c) &&
>> -	     IN4_ARE_ADDR_EQUAL(addr, inany_v4(&first_v4(c)->addr))) ||
>> -	    IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
>> +	if (IN4_ARE_ADDR_EQUAL(addr, &c->ip4.addr_seen))
>>   		return false;
>>   
>>   	return true;
>> @@ -535,11 +540,15 @@ static bool fwd_guest_accessible4(const struct ctx *c,
>>   static bool fwd_guest_accessible6(const struct ctx *c,
>>   				  const struct in6_addr *addr)
>>   {
>> +	const struct inany_addr_entry *e;
>> +
>>   	if (IN6_IS_ADDR_LOOPBACK(addr))
>>   		return false;
>>   
>> -	if (first_v6(c) && IN6_ARE_ADDR_EQUAL(addr, &first_v6(c)->addr.a6))
>> -		return false;
>> +	/* Check against all configured guest addresses */
>> +	for_each_addr(c, e, AF_INET6)
>> +		if (IN6_ARE_ADDR_EQUAL(addr, &e->addr.a6))
>> +			return false;
>>   
>>   	/* For IPv6, addr_seen starts unspecified, because we don't know what LL
>>   	 * address the guest will take until we see it.  Only check against it
>> @@ -714,7 +723,7 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
>>   		   first_v4(c) && inany_equals(addr, &first_v4(c)->addr)) {
>>   		*translated = inany_from_v4(c->ip4.map_guest_addr);
>>   	} else if (!IN6_IS_ADDR_UNSPECIFIED(&c->ip6.map_guest_addr) &&
>> -		   first_v6(c) && inany_equals6(addr, &first_v6(c)->addr.a6)) {
>> +		   first_v6(c) && inany_equals(addr, &first_v6(c)->addr)) {
>>   		translated->a6 = c->ip6.map_guest_addr;
>>   	} else if (fwd_guest_accessible(c, addr)) {
>>   		*translated = *addr;
>> -- 
>> 2.52.0
>>
>