[Virtio-fs] [PATCH 2/5] virtiofsd: create lock/pid file in per user cache dir

[Daniel Walsh]

On 7/29/20 18:14, Vivek Goyal wrote:
> Right now we create lock/pid file in /usr/local/var/... and unprivliged
> user does not have access to create files there.

Lock files should never be created in /usr, /usr should be considered
readonly.  Lock files should

always be created in /run or /tmp if /run is not writable.  As this PR
shows for rootless users XDG_RUNTIME_DIR

should be used.

> So create this file in per user cache dir as queried as specified
> by environment variable XDG_RUNTIME_DIR.
>
> Note: "su $USER" does not update XDG_RUNTIME_DIR and it still points to
> root user's director. So for now I create a directory /tmp/$UID to save
> lock/pid file. Dan pointed out that it can be a problem if a malicious
> app already has /tmp/$UID created. So we probably need to get rid of this.
>
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> ---
>  tools/virtiofsd/fuse_virtio.c | 40 ++++++++++++++++++++++++++++++-----
>  1 file changed, 35 insertions(+), 5 deletions(-)
>
> diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
> index 6b21a93841..f763a70ba5 100644
> --- a/tools/virtiofsd/fuse_virtio.c
> +++ b/tools/virtiofsd/fuse_virtio.c
> @@ -972,13 +972,43 @@ static bool fv_socket_lock(struct fuse_session *se)
>      g_autofree gchar *pidfile = NULL;
>      g_autofree gchar *dir = NULL;
>      Error *local_err = NULL;
> +    gboolean unprivileged = false;
>  
> -    dir = qemu_get_local_state_pathname("run/virtiofsd");
> +    if (geteuid() != 0)
> +        unprivileged = true;
>  
> -    if (g_mkdir_with_parents(dir, S_IRWXU) < 0) {
> -        fuse_log(FUSE_LOG_ERR, "%s: Failed to create directory %s: %s",
> -                 __func__, dir, strerror(errno));
> -        return false;
> +    /*
> +     * Unpriviliged users don't have access to /usr/local/var. Hence
> +     * store lock/pid file in per user directory. Use environment
> +     * variable XDG_RUNTIME_DIR.
> +     * If one logs into the system as root and then does "su" then
> +     * XDG_RUNTIME_DIR still points to root user directory. In that
> +     * case create a directory for user in /tmp/$UID
> +     */
> +    if (unprivileged) {
> +        gchar *user_dir = NULL;
> +        gboolean create_dir = false;
> +        user_dir = g_strdup(g_get_user_runtime_dir());
> +        if (!user_dir || g_str_has_suffix(user_dir, "/0")) {
> +            user_dir = g_strdup_printf("/tmp/%d", geteuid());
> +            create_dir = true;
> +        }
> +
> +        if (create_dir && g_mkdir_with_parents(user_dir, S_IRWXU) < 0) {
> +            fuse_log(FUSE_LOG_ERR, "%s: Failed to create directory %s: %s",
> +                     __func__, user_dir, strerror(errno));
> +            g_free(user_dir);
> +            return false;
> +        }
> +        dir = g_strdup(user_dir);
> +        g_free(user_dir);
> +    } else {
> +        dir = qemu_get_local_state_pathname("run/virtiofsd");
> +        if (g_mkdir_with_parents(dir, S_IRWXU) < 0) {
> +            fuse_log(FUSE_LOG_ERR, "%s: Failed to create directory %s: %s",
> +                     __func__, dir, strerror(errno));
> +            return false;
> +        }
>      }
>  
>      sk_name = g_strdup(se->vu_socket_path);