Libguestfs - Sep 2014 - [PATCH 1/2] builder, customize: disable SELinux

Having SELinux enabled (even if not enforcing) in the appliance causes
troubles to applications/libraries that read/write SELinux attributes.
---
 builder/builder.ml          | 6 +++++-
 customize/customize_main.ml | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/builder/builder.ml b/builder/builder.ml
index a407924..5195cfd 100644
--- a/builder/builder.ml
+++ b/builder/builder.ml
@@ -633,7 +633,11 @@ let main ()      (match smp with None -> () | Some smp
-> g#set_smp smp);
     g#set_network network;
 
-    g#set_selinux ops.flags.selinux_relabel;
+    (* Make sure to turn SELinux off to avoid awkward interactions
+     * between the appliance kernel and applications/libraries interacting
+     * with SELinux xattrs.
+     *)
+    g#set_selinux false;
 
     (* The output disk is being created, so use cache=unsafe here. *)
     g#add_drive_opts ~format:output_format ~cachemode:"unsafe"
output_filename;
diff --git a/customize/customize_main.ml b/customize/customize_main.ml
index 6e0ba2d..2c8b2ef 100644
--- a/customize/customize_main.ml
+++ b/customize/customize_main.ml
@@ -208,7 +208,11 @@ read the man page virt-customize(1).
     (match memsize with None -> () | Some memsize -> g#set_memsize
memsize);
     (match smp with None -> () | Some smp -> g#set_smp smp);
     g#set_network network;
-    g#set_selinux ops.flags.selinux_relabel;
+    (* Make sure to turn SELinux off to avoid awkward interactions
+     * between the appliance kernel and applications/libraries interacting
+     * with SELinux xattrs.
+     *)
+    g#set_selinux false;
 
     (* Add disks. *)
     add g dryrun;
-- 
1.9.3

When saving a configuration file, Augeas creates a new file and
replaces the old one with it; this creates a /etc/shadow file without
the SELinux xattrs, since they are missing.

Thus, create a temporary file with all the attributes of /etc/shadow, so
all the attributes of it (permissions and xattrs, among others) can be
restored properly on the new /etc/shadow.

As side effect, if a guest is already properly SELinux-labelled, then
there should be no more need to relabel it to make sure /etc/shadow
still has the right SELinux xattrs.
---
 customize/password.ml | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/customize/password.ml b/customize/password.ml
index 3437bf0..2bbfbbc 100644
--- a/customize/password.ml
+++ b/customize/password.ml
@@ -81,12 +81,19 @@ and read_password_from_file filename  (* Permissible
characters in a salt. *)
 let chars =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789./"
 
-let rec set_linux_passwords ~prog ?password_crypto g root passwords +let rec
set_linux_passwords ~prog ?password_crypto (g : Guestfs.guestfs) root passwords 
let crypto      match password_crypto with
     | None -> default_crypto ~prog g root
     | Some c -> c in
 
+  (* Create a (almost) empty temporary file with the attributes of
+   * /etc/shadow, so we can restore them later.
+   *)
+  let tempfile = g#mktemp "/etc/shadow.guestfsXXXXXX" in
+  g#write tempfile "*";
+  g#copy_attributes ~all:true "/etc/shadow" tempfile;
+
   g#aug_init "/" 0;
   let users = Array.to_list (g#aug_ls "/files/etc/shadow") in
   List.iter (
@@ -116,9 +123,11 @@ let rec set_linux_passwords ~prog ?password_crypto g root
passwords        with Not_found -> ()
   ) users;
   g#aug_save ();
+  g#aug_close ();
 
-  (* In virt-sysprep /.autorelabel will label it correctly. *)
-  g#chmod 0 "/etc/shadow"
+  (* Restore all the attributes from the temporary file, and remove it. *)
+  g#copy_attributes ~all:true tempfile "/etc/shadow";
+  g#rm tempfile
 
 (* Encrypt each password.  Use glibc (on the host).  See:
  *
https://rwmj.wordpress.com/2013/07/09/setting-the-root-or-other-passwords-in-a-linux-guest/
-- 
1.9.3

On Mon, Sep 29, 2014 at 01:57:24PM +0200, Pino Toscano
wrote:
> When saving a configuration file, Augeas creates a new file and
> replaces the old one with it; this creates a /etc/shadow file without
> the SELinux xattrs, since they are missing.
> 
> Thus, create a temporary file with all the attributes of /etc/shadow, so
> all the attributes of it (permissions and xattrs, among others) can be
> restored properly on the new /etc/shadow.
> 
> As side effect, if a guest is already properly SELinux-labelled, then
> there should be no more need to relabel it to make sure /etc/shadow
> still has the right SELinux xattrs.
> ---
>  customize/password.ml | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/customize/password.ml b/customize/password.ml
> index 3437bf0..2bbfbbc 100644
> --- a/customize/password.ml
> +++ b/customize/password.ml
> @@ -81,12 +81,19 @@ and read_password_from_file filename >  (*
Permissible characters in a salt. *)
>  let chars =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789./"
>  
> -let rec set_linux_passwords ~prog ?password_crypto g root passwords >
+let rec set_linux_passwords ~prog ?password_crypto (g : Guestfs.guestfs) root
passwords >    let crypto >      match password_crypto with
>      | None -> default_crypto ~prog g root
>      | Some c -> c in
>  
> +  (* Create a (almost) empty temporary file with the attributes of
> +   * /etc/shadow, so we can restore them later.
> +   *)
> +  let tempfile = g#mktemp "/etc/shadow.guestfsXXXXXX" in
> +  g#write tempfile "*";
> +  g#copy_attributes ~all:true "/etc/shadow" tempfile;
> +
>    g#aug_init "/" 0;
>    let users = Array.to_list (g#aug_ls "/files/etc/shadow") in
>    List.iter (
> @@ -116,9 +123,11 @@ let rec set_linux_passwords ~prog ?password_crypto g
root passwords >        with Not_found -> ()
>    ) users;
>    g#aug_save ();
> +  g#aug_close ();
>  
> -  (* In virt-sysprep /.autorelabel will label it correctly. *)
> -  g#chmod 0 "/etc/shadow"
> +  (* Restore all the attributes from the temporary file, and remove it. *)
> +  g#copy_attributes ~all:true tempfile "/etc/shadow";
> +  g#rm tempfile
>  
>  (* Encrypt each password.  Use glibc (on the host).  See:
>   *
https://rwmj.wordpress.com/2013/07/09/setting-the-root-or-other-passwords-in-a-linux-guest/
> -- 
> 1.9.3
ACK to both.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org