Re: [PATCH 06/10] Revert "conf: Adjust netmask on mismatch between IPv4 address/netmask and gateway"

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

[-- Attachment #1: Type: text/plain, Size: 2775 bytes --]

On Sun, May 14, 2023 at 08:14:11PM +0200, Stefano Brivio wrote:
> This reverts commit 7656a6f8888237b9e23d63666e921528b6aaf950: now, by
> default, we copy all the routes associated to the outbound interface
> into the routing table of the container, so there's no need for this
> horrible workaround anymore.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

This was never the right solution - even without the other
considerations raised by this series we probably should have
advertized an explicit host route to the gateway instead of mangling
the netmask.

> ---
>  conf.c | 25 +------------------------
>  1 file changed, 1 insertion(+), 24 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index c2a745e..3a2fc2d 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -634,9 +634,6 @@ static int conf_ip4_prefix(const char *arg)
>  static unsigned int conf_ip4(unsigned int ifi,
>  			     struct ip4_ctx *ip4, unsigned char *mac)
>  {
> -	in_addr_t addr, gw;
> -	int shift;
> -
>  	if (!ifi)
>  		ifi = nl_get_ext_if(AF_INET);
>  
> @@ -651,10 +648,8 @@ static unsigned int conf_ip4(unsigned int ifi,
>  	if (IN4_IS_ADDR_UNSPECIFIED(&ip4->addr))
>  		nl_addr(0, ifi, AF_INET, &ip4->addr, &ip4->prefix_len, NULL);
>  
> -	addr = ntohl(ip4->addr.s_addr);
> -	gw = ntohl(ip4->gw.s_addr);
> -
>  	if (!ip4->prefix_len) {
> +		in_addr_t addr = ntohl(ip4->addr.s_addr);
>  		if (IN_CLASSA(addr))
>  			ip4->prefix_len = (32 - IN_CLASSA_NSHIFT);
>  		else if (IN_CLASSB(addr))
> @@ -665,24 +660,6 @@ static unsigned int conf_ip4(unsigned int ifi,
>  			ip4->prefix_len = 32;
>  	}
>  
> -	/* We might get an address with a netmask that makes the default
> -	 * gateway unreachable, and in that case we would fail to configure
> -	 * the default route, with --config-net, or presumably a DHCP client
> -	 * in the guest or container would face the same issue.
> -	 *
> -	 * The host might have another route, to the default gateway itself,
> -	 * fixing the situation, but we only read default routes.
> -	 *
> -	 * Fix up the mask to allow reaching the default gateway from our
> -	 * configured address, if needed, and only if we find a non-zero
> -	 * mask that makes the gateway reachable.
> -	 */
> -	shift = 32 - ip4->prefix_len;
> -	while (shift < 32 && addr >> shift != gw >> shift)
> -		shift++;
> -	if (shift < 32)
> -		ip4->prefix_len = 32 - shift;
> -
>  	memcpy(&ip4->addr_seen, &ip4->addr, sizeof(ip4->addr_seen));
>  
>  	if (MAC_IS_ZERO(mac))

-- 
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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]