From bae6853906c388051a49b9a43776eba97e4f0523 Mon Sep 17 00:00:00 2001 From: Matthew Heon Date: Wed, 15 Jul 2020 15:25:12 -0400 Subject: Make changes to /etc/passwd on disk for non-read only Bind-mounting /etc/passwd into the container is problematic becuase of how system utilities like `useradd` work. They want to make a copy and then rename to try to prevent breakage; this is, unfortunately, impossible when the file they want to rename is a bind mount. The current behavior is fine for read-only containers, though, because we expect useradd to fail in those cases. Instead of bind-mounting, we can edit /etc/passwd in the container's rootfs. This is kind of gross, because the change will show up in `podman diff` and similar tools, and will be included in images made by `podman commit`. However, it's a lot better than breaking important system tools. Fixes #6953 Signed-off-by: Matthew Heon --- libpod/container_internal_linux.go | 48 ++++++++++++++++++++++++++++++++++---- 1 file changed, 43 insertions(+), 5 deletions(-) (limited to 'libpod') diff --git a/libpod/container_internal_linux.go b/libpod/container_internal_linux.go index 255505416..574525315 100644 --- a/libpod/container_internal_linux.go +++ b/libpod/container_internal_linux.go @@ -1458,11 +1458,26 @@ func (c *Container) generateCurrentUserPasswdEntry() (string, error) { if uid == 0 { return "", nil } + u, err := user.LookupId(strconv.Itoa(rootless.GetRootlessUID())) if err != nil { return "", errors.Wrapf(err, "failed to get current user") } - return fmt.Sprintf("%s:x:%s:%s:%s:%s:/bin/sh\n", u.Username, u.Uid, u.Gid, u.Username, c.WorkingDir()), nil + + // Lookup the user to see if it exists in the container image. + _, err = lookup.GetUser(c.state.Mountpoint, u.Username) + if err != User.ErrNoPasswdEntries { + return "", err + } + + // If the user's actual home directory exists, or was mounted in - use + // that. + homeDir := c.WorkingDir() + if MountExists(c.config.Spec.Mounts, u.HomeDir) { + homeDir = u.HomeDir + } + + return fmt.Sprintf("%s:x:%s:%s:%s:%s:/bin/sh\n", u.Username, u.Uid, u.Gid, u.Username, homeDir), nil } // generateUserPasswdEntry generates an /etc/passwd entry for the container user @@ -1488,12 +1503,9 @@ func (c *Container) generateUserPasswdEntry() (string, error) { // Lookup the user to see if it exists in the container image _, err = lookup.GetUser(c.state.Mountpoint, userspec) - if err != nil && err != User.ErrNoPasswdEntries { + if err != User.ErrNoPasswdEntries { return "", err } - if err == nil { - return "", nil - } if groupspec != "" { ugid, err := strconv.ParseUint(groupspec, 10, 32) @@ -1542,6 +1554,32 @@ func (c *Container) generatePasswd() (string, error) { if pwd == "" { return "", nil } + + // If we are *not* read-only - edit /etc/passwd in the container. + // This is *gross* (shows up in changes to the container, will be + // committed to images based on the container) but it actually allows us + // to add users to the container (a bind mount breaks useradd). + // We should never get here twice, because generateUserPasswdEntry will + // not return anything if the user already exists in /etc/passwd. + if !c.IsReadOnly() { + containerPasswd, err := securejoin.SecureJoin(c.state.Mountpoint, "/etc/passwd") + if err != nil { + return "", errors.Wrapf(err, "error looking up location of container %s /etc/passwd", c.ID()) + } + + f, err := os.OpenFile(containerPasswd, os.O_APPEND|os.O_WRONLY, 0600) + if err != nil { + return "", errors.Wrapf(err, "error opening container %s /etc/passwd", c.ID()) + } + defer f.Close() + + if _, err := f.WriteString(pwd); err != nil { + return "", errors.Wrapf(err, "unable to append to container %s /etc/passwd", c.ID()) + } + + return "", nil + } + originPasswdFile := filepath.Join(c.state.Mountpoint, "/etc/passwd") orig, err := ioutil.ReadFile(originPasswdFile) if err != nil && !os.IsNotExist(err) { -- cgit v1.2.3-54-g00ecf