[Dnsmasq-discuss] [PATCH] Change dhcp_release to use first address when no IP subnet matches

[Geert Stappers]

On 26-04-2019 22:03, Brian Haley wrote:

> Currently, dhcp_release will only send a 'fake' release
> when the address given is in the same subnet as an IP
> on the interface that was given.
>
> This doesn't work in an environment where dnsmasq is
> managing leases for remote subnets via a DHCP relay, as
> running dhcp_release locally will just cause it to
> silently exit without doing anything, leaving the lease
> n the database.
>
> Change it to save the first IP it finds on the interface,
> and if no matching subnet IP is found, use it as a fall-back.
> This fixes an issue we are seeing in certain Openstack
> deployments where we are using dnsmasq to provision baremetal
> systems in a datacenter.
>
> While using Dbus might have seemed like an obvious solution,
> because of our extensive use of network namespaces (which
> Dbus doesn't support), this seemed like a better solution
> than creating system.d policy files for each dnsmasq we
> might spawn and using --enable-dbus=$id in order to isolate
> messages to specific dnsmasq instances.
>
> Signed-off-by: Brian Haley <haleyb.dev at gmail.com>
> ---
>  contrib/lease-tools/dhcp_release.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/contrib/lease-tools/dhcp_release.c b/contrib/lease-tools/dhcp_release.c
> index 59883d4..63a732f 100644
> --- a/contrib/lease-tools/dhcp_release.c
> +++ b/contrib/lease-tools/dhcp_release.c
> @@ -180,6 +180,7 @@ static int is_same_net(struct in_addr a, struct in_addr b, struct in_addr mask)
>  
>  static struct in_addr find_interface(struct in_addr client, int fd, unsigned int index)
>  {
> +  struct in_addr first_addr = {};
>    struct sockaddr_nl addr;
>    struct nlmsghdr *h;
>    ssize_t len;
> @@ -218,7 +219,11 @@ static struct in_addr find_interface(struct in_addr client, int fd, unsigned int
>  
>        for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
>  	if (h->nlmsg_type == NLMSG_DONE)
> -	  exit(0);
> +          {
> +	    if (first_addr.s_addr)
> +	      return first_addr;
> +	    exit(0);
> +          }
>  	else if (h->nlmsg_type == RTM_NEWADDR)
>            {
>              struct ifaddrmsg *ifa = NLMSG_DATA(h);  
> @@ -234,7 +239,11 @@ static struct in_addr find_interface(struct in_addr client, int fd, unsigned int
>                  
>                  for (rta = IFA_RTA(ifa); RTA_OK(rta, len1); rta = RTA_NEXT(rta, len1))
>  		  if (rta->rta_type == IFA_LOCAL)
> -		    addr = *((struct in_addr *)(rta+1));
> +		    {
> +		      addr = *((struct in_addr *)(rta+1));
> +		      if (!first_addr.s_addr)
> +			first_addr = addr;
> +		    }
>  		
>                  if (addr.s_addr && is_same_net(addr, client, netmask))
>  		  return addr;


FWIW   above patch had no review yet