From 639fdf06edecfa0f61eaa55753edb6f3fae9fcef Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 20 Mar 2024 16:33:39 +1100 Subject: [PATCH] netlink: Fix selection of template interface Since f919dc7a4b1c ("conf, netlink: Don't require a default route to start"), if there is only one host interface with routes, we will pick that as the template interface, even if there are no default routes for an IP version. Unfortunately this selection had a serious flaw: in some cases it would 'return' in the middle of an nl_foreach() loop, meaning we wouldn't consume all the netlink responses for our query. This could cause later netlink operations to fail as we read leftover responses from the aborted query. Rewrite the interface detection to avoid this problem. While we're there: * Perform detection of both default and non-default routes in a single pass, avoiding an ugly goto * Give more detail on error and working but unusual paths about the situation (no suitable interface, multiple possible candidates, etc.). Fixes: f919dc7a4b1c ("conf, netlink: Don't require a default route to start") Link: https://bugs.passt.top/show_bug.cgi?id=83 Link: https://github.com/containers/podman/issues/22052 Link: https://bugzilla.redhat.com/show_bug.cgi?id=2270257 Signed-off-by: David Gibson [sbrivio: Use info(), not warn() for somewhat expected cases where one IP version has no default routes, or no routes at all] Signed-off-by: Stefano Brivio --- conf.c | 4 ++-- netlink.c | 64 +++++++++++++++++++++++++++++++++---------------------- 2 files changed, 41 insertions(+), 27 deletions(-) diff --git a/conf.c b/conf.c index 644752c..9e0318a 100644 --- a/conf.c +++ b/conf.c @@ -584,7 +584,7 @@ static unsigned int conf_ip4(unsigned int ifi, ifi = nl_get_ext_if(nl_sock, AF_INET); if (!ifi) { - info("No interface with a route for IPv4: disabling IPv4"); + info("Couldn't pick external interface: disabling IPv4"); return 0; } @@ -656,7 +656,7 @@ static unsigned int conf_ip6(unsigned int ifi, ifi = nl_get_ext_if(nl_sock, AF_INET6); if (!ifi) { - info("No interface with a route for IPv6: disabling IPv6"); + info("Couldn't pick external interface: disabling IPv6"); return 0; } diff --git a/netlink.c b/netlink.c index 632304c..9b3dba2 100644 --- a/netlink.c +++ b/netlink.c @@ -254,8 +254,8 @@ unsigned int nl_get_ext_if(int s, sa_family_t af) .rtm.rtm_type = RTN_UNICAST, .rtm.rtm_family = af, }; - bool default_only = true; - unsigned int ifi = 0; + unsigned defifi = 0, anyifi = 0; + unsigned ndef = 0, nany = 0; struct nlmsghdr *nh; struct rtattr *rta; char buf[NLBUFSIZ]; @@ -263,7 +263,6 @@ unsigned int nl_get_ext_if(int s, sa_family_t af) uint32_t seq; size_t na; -again: /* Look for an interface with a default route first, failing that, look * for any interface with a route, and pick it only if it's the only * interface with a route. @@ -271,46 +270,61 @@ again: seq = nl_send(s, &req, RTM_GETROUTE, NLM_F_DUMP, sizeof(req)); nl_foreach_oftype(nh, status, s, buf, seq, RTM_NEWROUTE) { struct rtmsg *rtm = (struct rtmsg *)NLMSG_DATA(nh); + unsigned thisifi = 0; - if (default_only) { - if (ifi || rtm->rtm_dst_len || rtm->rtm_family != af) - continue; - } else { - if (rtm->rtm_family != af) - continue; - } + if (rtm->rtm_family != af) + continue; for (rta = RTM_RTA(rtm), na = RTM_PAYLOAD(nh); RTA_OK(rta, na); rta = RTA_NEXT(rta, na)) { if (rta->rta_type == RTA_OIF) { - if (!default_only && ifi && - ifi != *(unsigned int *)RTA_DATA(rta)) - return 0; - - ifi = *(unsigned int *)RTA_DATA(rta); + thisifi = *(unsigned int *)RTA_DATA(rta); } else if (rta->rta_type == RTA_MULTIPATH) { const struct rtnexthop *rtnh; rtnh = (struct rtnexthop *)RTA_DATA(rta); - - if (!default_only && ifi && - (int)ifi != rtnh->rtnh_ifindex) - return 0; - - ifi = rtnh->rtnh_ifindex; + thisifi = rtnh->rtnh_ifindex; } } + + if (!thisifi) + continue; /* No interface for this route */ + + if (rtm->rtm_dst_len == 0) { + /* Default route */ + ndef++; + if (!defifi) + defifi = thisifi; + } else { + /* Non-default route */ + nany++; + if (!anyifi) + anyifi = thisifi; + } } if (status < 0) warn("netlink: RTM_GETROUTE failed: %s", strerror(-status)); - if (!ifi && default_only) { - default_only = false; - goto again; + if (defifi) { + if (ndef > 1) + info("Multiple default %s routes, picked first", + af == AF_INET ? "IPv4" : "IPv6"); + return defifi; } - return ifi; + if (anyifi) { + if (nany == 1) + return anyifi; + + info("Multiple interfaces with %s routes, use -i to select one", + af == AF_INET ? "IPv4" : "IPv6"); + } + + if (!nany) + info("No interfaces with %s routes", af == AF_INET ? "IPv4" : "IPv6"); + + return 0; } /**