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treewide: Introduce 'local mode' for disconnected setups

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There are setups where no host interface is available or configured
at all, intentionally or not, temporarily or not, but users expect
(Podman) containers to run in any case as they did with slirp4netns,
and we're now getting reports that we broke such setups at a rather
alarming rate.

To this end, if we don't find any usable host interface, instead of
exiting:

- for IPv4, use 169.254.2.1 as guest/container address and 169.254.2.2
  as default gateway

- for IPv6, don't assign any address (forcibly disable DHCPv6), and
  use the *first* link-local address we observe to represent the
  guest/container. Advertise fe80::1 as default gateway

- use 'tap0' as default interface name for pasta

Change ifi4 and ifi6 in struct ctx to int and accept a special -1
value meaning that no host interface was selected, but the IP family
is enabled. The fact that the kernel uses unsigned int values for
those is not an issue as 1. one can't create so many interfaces
anyway and 2. we otherwise handle those values transparently.

Fix a botched conditional in conf_print() to actually skip printing
DHCPv6 information if DHCPv6 is disabled (and skip printing NDP
information if NDP is disabled).

Link: https://github.com/containers/podman/issues/24614
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2024-11-22 07:57:43 +01:00
commit 14b84a7f07
5 changed files with 116 additions and 32 deletions

8
passt.h
View file

@ -202,10 +202,10 @@ struct ip6_ctx {
* @our_tap_mac: Pasta/passt's MAC on the tap link
* @guest_mac: MAC address of guest or namespace, seen or configured
* @hash_secret: 128-bit secret for siphash functions
* @ifi4: Index of template interface for IPv4, 0 if IPv4 disabled
* @ifi4: Template interface for IPv4, -1: none, 0: IPv4 disabled
* @ip: IPv4 configuration
* @dns_search: DNS search list
* @ifi6: Index of template interface for IPv6, 0 if IPv6 disabled
* @ifi6: Template interface for IPv6, -1: none, 0: IPv6 disabled
* @ip6: IPv6 configuration
* @pasta_ifn: Name of namespace interface for pasta
* @pasta_ifi: Index of namespace interface for pasta
@ -258,12 +258,12 @@ struct ctx {
unsigned char guest_mac[ETH_ALEN];
uint64_t hash_secret[2];
unsigned int ifi4;
int ifi4;
struct ip4_ctx ip4;
struct fqdn dns_search[MAXDNSRCH];
unsigned int ifi6;
int ifi6;
struct ip6_ctx ip6;
char pasta_ifn[IF_NAMESIZE];