Re: [PATCH] libselinux: fix selinux_restorecon() statfs bug

[Stephen Smalley <stephen.smalley.work@gmail.com>]

On Thu, Jun 4, 2020 at 4:08 PM Stephen Smalley
<stephen.smalley.work@gmail.com> wrote:
>
> As reported in https://github.com/SELinuxProject/selinux/issues/248,
> setfiles -r (rootpath) fails when the alternate root contains a symlink
> that is correct relative to the alternate root but not in the current root.
> This is a regression introduced by commit e016502c0a26 ("libselinux: Save
> digest of all partial matches for directory").  Do not call statfs(2) here
> if acting on a symbolic link.  Unfortunately there is no lstatfs() call.
> Ensure that we initialize the statfs buffer always.  If the supplied
> file is a symlink, then we don't need to worry about the later tests of
> filesystem type because we wouldn't be setting the digest anyway and
> we are not performing a full sysfs relabel.  While here, fix the earlier
> test for a directory to use the correct test.
>
> Reproducer:
> $ mkdir /root/my-chroot && echo foo > /root/my-chroot/link-target && ln -s /link-target /root/my-chroot/symlink
> $ echo "/root/my-chroot/symlink" | setfiles -vFi -r /root/my-chroot -f - /etc/selinux/targeted/contexts/files/file_contexts
>
> Before:
> setfiles: statfs(/root/my-chroot/symlink) failed: No such file or directory
>
> After:
> Relabeled /root/my-chroot/symlink from unconfined_u:object_r:admin_home_t:s0 to system_u:object_r:default_t:s0
>
> Fixes: https://github.com/SELinuxProject/selinux/issues/248
> Fixes: e016502c0a26 ("libselinux: Save digest of all partial matches for directory")
> Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>

Anyone want to ack or object to this patch?

> ---
>  libselinux/src/selinux_restorecon.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/libselinux/src/selinux_restorecon.c b/libselinux/src/selinux_restorecon.c
> index 91dfeb66..d1ce830c 100644
> --- a/libselinux/src/selinux_restorecon.c
> +++ b/libselinux/src/selinux_restorecon.c
> @@ -938,7 +938,7 @@ int selinux_restorecon(const char *pathname_orig,
>         }
>
>         /* Skip digest if not a directory */
> -       if ((sb.st_mode & S_IFDIR) != S_IFDIR)
> +       if (!S_ISDIR(sb.st_mode))
>                 setrestorecondigest = false;
>
>         if (!flags.recurse) {
> @@ -952,7 +952,8 @@ int selinux_restorecon(const char *pathname_orig,
>         }
>
>         /* Obtain fs type */
> -       if (statfs(pathname, &sfsb) < 0) {
> +       memset(&sfsb, 0, sizeof sfsb);
> +       if (!S_ISLNK(sb.st_mode) && statfs(pathname, &sfsb) < 0) {
>                 selinux_log(SELINUX_ERROR,
>                             "statfs(%s) failed: %s\n",
>                             pathname, strerror(errno));
> --
> 2.23.3
>