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[164.138.29.33]) by smtp.gmail.com with ESMTPSA id s10-20020a1709060c0a00b00a44899a44ddsm7263931ejf.11.2024.03.20.04.03.20 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 Mar 2024 04:03:21 -0700 (PDT) Date: Wed, 20 Mar 2024 12:02:43 +0100 From: Stefano Brivio To: Paul Holzinger Subject: Re: [PATCH] netlink: Fix selection of template interface Message-ID: <20240320120243.49516b90@elisabeth> In-Reply-To: <80107179-5357-4b14-94ae-c82925a97ba8@redhat.com> References: <20240320053339.553418-1-david@gibson.dropbear.id.au> <80107179-5357-4b14-94ae-c82925a97ba8@redhat.com> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.36; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: 2BVUWIHZUXADKEZUALLQTK55I4KOC7G7 X-Message-ID-Hash: 2BVUWIHZUXADKEZUALLQTK55I4KOC7G7 X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: David Gibson , passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Wed, 20 Mar 2024 11:51:59 +0100 Paul Holzinger wrote: > On 20/03/2024 06:33, David Gibson wrote: > > 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 > > --- > > conf.c | 4 ++-- > > netlink.c | 62 ++++++++++++++++++++++++++++++++++--------------------- > > 2 files changed, 40 insertions(+), 26 deletions(-) > > > > diff --git a/conf.c b/conf.c > > index 644752cc..9e0318a5 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 632304c1..c0a5f158 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); > > + thisifi = rtnh->rtnh_ifindex; > > + } > > + } > > > > - if (!default_only && ifi && > > - (int)ifi != rtnh->rtnh_ifindex) > > - return 0; > > + if (!thisifi) > > + continue; /* No interface for this route */ > > > > - ifi = rtnh->rtnh_ifindex; > > - } > > + 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; > > + > > + warn("Multiple interfaces with %s routes, use -i to select one", > > + af == AF_INET ? "IPv4" : "IPv6"); > > This should not be a warning, for me this always triggers because I have > two interfaces with link local addresses and no global ipv6 route as I > do not have any ipv6 connection. I was about to reply as I just applied this with s/warn/info/ here :) > Or maybe the correct fix is to never consider ipv6 link local routes for > this logic? At least I cannot see the purpose of using a interface with > only a link local route. > > > + } > > + > > + if (!nany) > > + warn("No interfaces with %s routes", af == AF_INET ? "IPv4" : "IPv6"); ...and here, because if one has no IPv6 routes we would reintroduce the issue we just fixed in 338b6321ac0d ("conf: No routable interface for IPv4 or IPv6 is informational, not a warning"). I think the purpose of picking interfaces based on routes for link-local destinations is for practical test setups like the one described in https://github.com/containers/podman/issues/21896. Functionally it doesn't make sense, but it shouldn't harm either (right?). > > + > > + return 0; > > } > > > > /** > I reproduced by having a second interface and confirm this patch fixes it. Thanks for checking! Let's hope that was the case in the failing test. -- Stefano