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network/dhcp4: accept local subnet routes from DHCP

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RFC3442 specifies option 121 (Classless Static Routes) that allow a DHCP
server to push arbitrary routes to a client. It has a Local Subnet
Routes section expliciting the behavior of routes with a null (0.0.0.0)
gateway.

Such routes are to be installed on the interface with a Link scope, to
mark them as directly available on the link without any gateway.

Networkd currently drops those routes, which is against the RFC, as
Linux has proper support for such routes.

Fixes: 7f20627 ("network: dhcp4: ignore gateway in static routes if destination is link-local or in the same network")
(cherry picked from commit 1d84a3c779)
This commit is contained in:
Tuetuopay 2023-01-27 15:10:49 +01:00 committed by Luca Boccassi
parent b71ade8779
commit b0f514ba56
1 changed files with 11 additions and 8 deletions
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19
src/network/networkd-dhcp4.c
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@ -334,15 +334,18 @@ static int dhcp4_request_route_auto(
route->gw = IN_ADDR_NULL;
route->prefsrc.in = address;
} else {
if (in4_addr_is_null(gw)) {
log_link_debug(link, "DHCP: requested route destination "IPV4_ADDRESS_FMT_STR"/%u is not in the assigned network "
IPV4_ADDRESS_FMT_STR"/%u, but no gateway is specified, ignoring.",
IPV4_ADDRESS_FMT_VAL(route->dst.in), route->dst_prefixlen,
IPV4_ADDRESS_FMT_VAL(prefix), prefixlen);
return 0;
}
} else if (in4_addr_is_null(gw)) {
log_link_debug(link, "DHCP: requested route destination "IPV4_ADDRESS_FMT_STR"/%u is not in the assigned network "
IPV4_ADDRESS_FMT_STR"/%u, but no gateway is specified, using 'link' scope.",
IPV4_ADDRESS_FMT_VAL(route->dst.in), route->dst_prefixlen,
IPV4_ADDRESS_FMT_VAL(prefix), prefixlen);
route->scope = RT_SCOPE_LINK;
route->gw_family = AF_UNSPEC;
route->gw = IN_ADDR_NULL;
route->prefsrc.in = address;
} else {
r = dhcp4_request_route_to_gateway(link, gw);
if (r < 0)
return r;