From 2a8c4144887373dd8c070ac09f33fea7ab764a95 Mon Sep 17 00:00:00 2001 From: Paul Holzinger Date: Mon, 16 Aug 2021 11:03:16 +0200 Subject: Fix rootless cni dns without systemd stub resolver When a host uses systemd-resolved but not the resolved stub resolver the following symlinks are created: `/etc/resolv.conf` -> `/run/systemd/resolve/stub-resolv.conf` -> `/run/systemd/resolve/resolv.conf`. Because the code uses filepath.EvalSymlinks we put the new resolv.conf to `/run/systemd/resolve/resolv.conf` but the `/run/systemd/resolve/stub-resolv.conf` link does not exists in the mount ns. To fix this we will walk the symlinks manually until we reach the first one under `/run` and use this for the resolv.conf file destination. This fixes a regression which was introduced in e73d4829900c. Fixes #11222 Signed-off-by: Paul Holzinger --- libpod/networking_linux.go | 24 ++++++++++++++++++++---- test/system/500-networking.bats | 3 +++ 2 files changed, 23 insertions(+), 4 deletions(-) diff --git a/libpod/networking_linux.go b/libpod/networking_linux.go index 17e444f66..2ed2bb01b 100644 --- a/libpod/networking_linux.go +++ b/libpod/networking_linux.go @@ -173,11 +173,27 @@ func (r *RootlessCNI) Do(toRun func() error) error { // the link target will be available in the mount ns. // see: https://github.com/containers/podman/issues/10855 resolvePath := "/etc/resolv.conf" - resolvePath, err = filepath.EvalSymlinks(resolvePath) - if err != nil { - return err + for i := 0; i < 255; i++ { + // Do not use filepath.EvalSymlinks, we only want the first symlink under /run. + // If /etc/resolv.conf has more than one symlink under /run, e.g. + // -> /run/systemd/resolve/stub-resolv.conf -> /run/systemd/resolve/resolv.conf + // we would put the netns resolv.conf file to the last path. However this will + // break dns because the second link does not exists in the mount ns. + // see https://github.com/containers/podman/issues/11222 + link, err := os.Readlink(resolvePath) + if err != nil { + // if there is no symlink exit + break + } + resolvePath = filepath.Join(filepath.Dir(resolvePath), link) + if strings.HasPrefix(resolvePath, "/run/") { + break + } + if i == 254 { + return errors.New("too many symlinks while resolving /etc/resolv.conf") + } } - logrus.Debugf("The actual path of /etc/resolv.conf on the host is %q", resolvePath) + logrus.Debugf("The path of /etc/resolv.conf in the mount ns is %q", resolvePath) // When /etc/resolv.conf on the host is a symlink to /run/systemd/resolve/stub-resolv.conf, // we have to mount an empty filesystem on /run/systemd/resolve in the child namespace, // so as to isolate the directory from the host mount namespace. diff --git a/test/system/500-networking.bats b/test/system/500-networking.bats index 6ffee7eaf..3ebe45e63 100644 --- a/test/system/500-networking.bats +++ b/test/system/500-networking.bats @@ -210,6 +210,9 @@ load helpers $IMAGE nc -l -n -v -p $myport cid="$output" + # check that dns is working inside the container + run_podman exec $cid nslookup google.com + # emit random string, and check it teststring=$(random_string 30) echo "$teststring" | nc 127.0.0.1 $myport -- cgit v1.2.3-54-g00ecf