Libguestfs - Nov 2020 - Re: [common PATCH 0/3] SELinux_relabel: relabel only if enforcing (RHBZ#1828952)

Continuation/rework of:
https://www.redhat.com/archives/libguestfs/2020-May/msg00020.html

This is my approach, as I explained here:
https://bugzilla.redhat.com/show_bug.cgi?id=1828952#c4
https://www.redhat.com/archives/libguestfs/2020-May/msg00035.html
IOW: do not attempt to relabel if the guest is not enforcing, as it is
either useless or may fail; few words more are in the comments of patch
#3.

Pino Toscano (2):
  mlcustomize: refactor reading from /etc/selinux/config
  mlcustomize: do not relabel if not enforcing (RHBZ#1828952)

Richard W.M. Jones (1):
  mlcustomize: Refactor SELinux_relabel code.

 mlcustomize/SELinux_relabel.ml | 153 ++++++++++++++++++++-------------
 1 file changed, 94 insertions(+), 59 deletions(-)

-- 
2.26.2

From: "Richard W.M. Jones" <rjones@redhat.com>

This shouldn't change the effect of this code.
---
 mlcustomize/SELinux_relabel.ml | 121 ++++++++++++++++++---------------
 1 file changed, 65 insertions(+), 56 deletions(-)

diff --git a/mlcustomize/SELinux_relabel.ml b/mlcustomize/SELinux_relabel.ml
index 44995df..5df1f08 100644
--- a/mlcustomize/SELinux_relabel.ml
+++ b/mlcustomize/SELinux_relabel.ml
@@ -28,65 +28,74 @@ module G = Guestfs
 let array_find a l    List.mem a (Array.to_list l)
 
-let relabel (g : G.guestfs) -  (* Is the guest using SELinux? *)
-  if g#is_file ~followsymlinks:true "/usr/sbin/load_policy"
&&
-     g#is_file ~followsymlinks:true "/etc/selinux/config" then (
-    (* Is setfiles / SELinux relabelling functionality available? *)
-    if g#feature_available [| "selinuxrelabel" |] then (
-      (* Use Augeas to parse /etc/selinux/config. *)
-      g#aug_init "/" (16+32) (* AUG_SAVE_NOOP | AUG_NO_LOAD *);
-      (* See: https://bugzilla.redhat.com/show_bug.cgi?id=975412#c0 *)
-      ignore (g#aug_rm "/augeas/load/*[\"/etc/selinux/config/\"
!~ regexp('^') + glob(incl) + regexp('/.*')]");
-      g#aug_load ();
-      debug_augeas_errors g;
-
-      (* Get the SELinux policy name, eg. "targeted",
"minimum".
-       * Use "targeted" if not specified, just like libselinux does.
+let rec relabel (g : G.guestfs) +  (* Is the guest using SELinux?  (Otherwise
this is a no-op). *)
+  if is_selinux_guest g then (
+    try
+      use_setfiles g;
+      (* That worked, so we don't need to autorelabel. *)
+      g#rm_f "/.autorelabel"
+    with Failure _ ->
+      (* This is the fallback in case something in the setfiles
+       * method didn't work.  That includes the case where a non-SELinux
+       * host is processing an SELinux guest, and other things.
        *)
-      let policy -        let config_path =
"/files/etc/selinux/config" in
-        let selinuxtype_path = config_path ^ "/SELINUXTYPE" in
-        let keys = g#aug_ls config_path in
-        if array_find selinuxtype_path keys then
-          g#aug_get selinuxtype_path
-        else
-          "targeted" in
+      g#touch "/.autorelabel"
+  )
 
-      g#aug_close ();
+and is_selinux_guest g +  g#is_file ~followsymlinks:true
"/usr/sbin/load_policy" &&
+  g#is_file ~followsymlinks:true "/etc/selinux/config"
 
-      (* Get the spec file name. *)
-      let specfile -        sprintf
"/etc/selinux/%s/contexts/files/file_contexts" policy in
+and use_setfiles g +  (* Is setfiles / SELinux relabelling functionality
available? *)
+  if not (g#feature_available [| "selinuxrelabel" |]) then
+    failwith "no selinux relabel feature";
 
-      (* RHEL 6.2 - 6.5 had a malformed specfile that contained the
-       * invalid regular expression "/var/run/spice-vdagentd.\pid"
-       * (instead of "\.p").  This stops setfiles from working on
-       * the guest.
-       *
-       * Because an SELinux relabel writes all over the filesystem,
-       * it seems reasonable to fix this problem in the specfile
-       * at the same time.  (RHBZ#1374232)
-       *)
-      if g#grep ~fixed:true "vdagentd.\\pid" specfile <> [||]
then (
-        debug "fixing invalid regular expression in %s" specfile;
-        let old_specfile = specfile ^ "~" in
-        g#mv specfile old_specfile;
-        let content = g#read_file old_specfile in
-        let content -          String.replace content
"vdagentd.\\pid" "vdagentd\\.pid" in
-        g#write specfile content;
-        g#copy_attributes ~all:true old_specfile specfile
-      );
+  (* Use Augeas to parse /etc/selinux/config. *)
+  g#aug_init "/" (16+32) (* AUG_SAVE_NOOP | AUG_NO_LOAD *);
+  (* See: https://bugzilla.redhat.com/show_bug.cgi?id=975412#c0 *)
+  ignore (g#aug_rm "/augeas/load/*[\"/etc/selinux/config/\" !~
regexp('^') + glob(incl) + regexp('/.*')]");
+  g#aug_load ();
+  debug_augeas_errors g;
 
-      (* Relabel everything. *)
-      g#selinux_relabel ~force:true specfile "/";
+  (* Get the SELinux policy name, eg. "targeted",
"minimum".
+   * Use "targeted" if not specified, just like libselinux does.
+   *)
+  let policy +    let config_path = "/files/etc/selinux/config" in
+    let selinuxtype_path = config_path ^ "/SELINUXTYPE" in
+    let keys = g#aug_ls config_path in
+    if array_find selinuxtype_path keys then
+      g#aug_get selinuxtype_path
+    else
+      "targeted" in
 
-      (* If that worked, we don't need to autorelabel. *)
-      g#rm_f "/.autorelabel"
-    )
-    else (
-      (* SELinux guest, but not SELinux host.  Fallback to this. *)
-      g#touch "/.autorelabel"
-    )
-  )
+  g#aug_close ();
+
+  (* Get the spec file name. *)
+  let specfile +    sprintf
"/etc/selinux/%s/contexts/files/file_contexts" policy in
+
+  (* RHEL 6.2 - 6.5 had a malformed specfile that contained the
+   * invalid regular expression "/var/run/spice-vdagentd.\pid"
+   * (instead of "\.p").  This stops setfiles from working on
+   * the guest.
+   *
+   * Because an SELinux relabel writes all over the filesystem,
+   * it seems reasonable to fix this problem in the specfile
+   * at the same time.  (RHBZ#1374232)
+   *)
+  if g#grep ~fixed:true "vdagentd.\\pid" specfile <> [||] then
(
+    debug "fixing invalid regular expression in %s" specfile;
+    let old_specfile = specfile ^ "~" in
+    g#mv specfile old_specfile;
+    let content = g#read_file old_specfile in
+    let content +      String.replace content "vdagentd.\\pid"
"vdagentd\\.pid" in
+    g#write specfile content;
+    g#copy_attributes ~all:true old_specfile specfile
+  );
+
+  (* Relabel everything. *)
+  g#selinux_relabel ~force:true specfile "/"
-- 
2.26.2

Move the reading of values from /etc/selinux/config to an own function,
so it can be easily reused.

This is a simple refactoring.
---
 mlcustomize/SELinux_relabel.ml | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/mlcustomize/SELinux_relabel.ml b/mlcustomize/SELinux_relabel.ml
index 5df1f08..647aeda 100644
--- a/mlcustomize/SELinux_relabel.ml
+++ b/mlcustomize/SELinux_relabel.ml
@@ -62,14 +62,7 @@ and use_setfiles g    (* Get the SELinux policy name, eg.
"targeted", "minimum".
    * Use "targeted" if not specified, just like libselinux does.
    *)
-  let policy -    let config_path = "/files/etc/selinux/config" in
-    let selinuxtype_path = config_path ^ "/SELINUXTYPE" in
-    let keys = g#aug_ls config_path in
-    if array_find selinuxtype_path keys then
-      g#aug_get selinuxtype_path
-    else
-      "targeted" in
+  let policy = read_selinux_config_key g "SELINUXTYPE"
"targeted" in
 
   g#aug_close ();
 
@@ -99,3 +92,12 @@ and use_setfiles g  
   (* Relabel everything. *)
   g#selinux_relabel ~force:true specfile "/"
+
+and read_selinux_config_key g key defval +  let config_path =
"/files/etc/selinux/config" in
+  let key_path = config_path ^ "/" ^ key in
+  let keys = g#aug_ls config_path in
+  if array_find key_path keys then
+    g#aug_get key_path
+  else
+    defval
-- 
2.26.2

Do not attempt to relabel a guest in case its SELinux enforcing mode is
not "enforcing", as it is either pointless, or it may fail because of
an
invalid policy configured.
---
 mlcustomize/SELinux_relabel.ml | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/mlcustomize/SELinux_relabel.ml b/mlcustomize/SELinux_relabel.ml
index 647aeda..db00e59 100644
--- a/mlcustomize/SELinux_relabel.ml
+++ b/mlcustomize/SELinux_relabel.ml
@@ -24,6 +24,9 @@ open Printf
 
 module G = Guestfs
 
+exception SELinux_not_enforcing
+(* Interal exception to signal a non-enforcing SELinux. *)
+
 (* Simple reimplementation of Array.mem, available only with OCaml >= 4.03.
*)
 let array_find a l    List.mem a (Array.to_list l)
@@ -35,12 +38,18 @@ let rec relabel (g : G.guestfs)        use_setfiles g;
       (* That worked, so we don't need to autorelabel. *)
       g#rm_f "/.autorelabel"
-    with Failure _ ->
+    with
+    | Failure _ ->
       (* This is the fallback in case something in the setfiles
        * method didn't work.  That includes the case where a non-SELinux
        * host is processing an SELinux guest, and other things.
        *)
       g#touch "/.autorelabel"
+    | SELinux_not_enforcing ->
+      (* This means that SELinux was not configured to be in enforcing mode,
+       * so silently accept this.
+       *)
+      ()
   )
 
 and is_selinux_guest g @@ -59,6 +68,21 @@ and use_setfiles g    g#aug_load ();
   debug_augeas_errors g;
 
+  (* Get the SELinux enforcing mode, eg "enforcing",
"permissive",
+   * "disabled".
+   * Use "disabled" if not specified, just like libselinux seems to
do.
+   *)
+  let typ = read_selinux_config_key g "SELINUX" "disabled"
in
+  (* Do not attempt any relabelling if the SELinux is not
"enforcing":
+   * - in "permissive" mode SELinux is still running, however nothing
is
+   *   enforced: this means labels can be wrong, and "it is fine"
+   * - when "disabled" means SELinux is not running, so any
relabelling
+   *   is pointless (other than potentially fail due to an invalid
+   *   SELINUXTYPE configuration)
+   *)
+  if typ <> "enforcing" then
+    raise SELinux_not_enforcing;
+
   (* Get the SELinux policy name, eg. "targeted",
"minimum".
    * Use "targeted" if not specified, just like libselinux does.
    *)
-- 
2.26.2

On Wed, Sep 23, 2020 at 05:57:50PM +0200, Pino Toscano
wrote:
> Do not attempt to relabel a guest in case its SELinux enforcing mode is
> not "enforcing", as it is either pointless, or it may fail
because of an
> invalid policy configured.
> ---
>  mlcustomize/SELinux_relabel.ml | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/mlcustomize/SELinux_relabel.ml
b/mlcustomize/SELinux_relabel.ml
> index 647aeda..db00e59 100644
> --- a/mlcustomize/SELinux_relabel.ml
> +++ b/mlcustomize/SELinux_relabel.ml
> @@ -24,6 +24,9 @@ open Printf
>  
>  module G = Guestfs
>  
> +exception SELinux_not_enforcing
> +(* Interal exception to signal a non-enforcing SELinux. *)
> +
>  (* Simple reimplementation of Array.mem, available only with OCaml >=
4.03. *)
>  let array_find a l >    List.mem a (Array.to_list l)
> @@ -35,12 +38,18 @@ let rec relabel (g : G.guestfs) >       
use_setfiles g;
>        (* That worked, so we don't need to autorelabel. *)
>        g#rm_f "/.autorelabel"
> -    with Failure _ ->
> +    with
> +    | Failure _ ->
>        (* This is the fallback in case something in the setfiles
>         * method didn't work.  That includes the case where a
non-SELinux
>         * host is processing an SELinux guest, and other things.
>         *)
>        g#touch "/.autorelabel"
> +    | SELinux_not_enforcing ->
> +      (* This means that SELinux was not configured to be in enforcing
mode,
> +       * so silently accept this.
> +       *)
> +      ()
>    )
>  
>  and is_selinux_guest g > @@ -59,6 +68,21 @@ and use_setfiles g >   
g#aug_load ();
>    debug_augeas_errors g;
>  
> +  (* Get the SELinux enforcing mode, eg "enforcing",
"permissive",
> +   * "disabled".
> +   * Use "disabled" if not specified, just like libselinux seems
to do.
> +   *)
> +  let typ = read_selinux_config_key g "SELINUX"
"disabled" in
> +  (* Do not attempt any relabelling if the SELinux is not
"enforcing":
> +   * - in "permissive" mode SELinux is still running, however
nothing is
> +   *   enforced: this means labels can be wrong, and "it is
fine"
I don't think it's fine.  As I showed here:

https://www.redhat.com/archives/libguestfs/2020-June/msg00115.html

in permissive mode labels are still being updated on disk.

TBH I don't understand what you said here:

https://www.redhat.com/archives/libguestfs/2020-June/msg00117.html

about "both the labels and the policy may be all wrong".  If the
administrator set the policy to permissive then labels ought still to
be updated when the guest is running, and we ought to try to keep them
updated if we can in v2v.  It's also fine for an administrator to
switch a system to permissive and then back to enforcing without
relabelling or rebooting.
> +   * - when "disabled" means SELinux is not running, so any
relabelling
> +   *   is pointless (other than potentially fail due to an invalid
> +   *   SELINUXTYPE configuration)
Here you're correct.  Once the admin disabled SELinux, labels are
going to quickly get out of step with reality, and so attempting to
relabel in virt-v2v is indeed a waste of time.

I'd accept this series if you changed "not enforcing" to
"not enforcing or permissive".

Rich.
> +   *)
> +  if typ <> "enforcing" then
> +    raise SELinux_not_enforcing;
> +
>    (* Get the SELinux policy name, eg. "targeted",
"minimum".
>     * Use "targeted" if not specified, just like libselinux does.
>     *)
> -- 
> 2.26.2
> 
> _______________________________________________
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> Libguestfs@redhat.com
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-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v

On Wednesday, 23 September 2020 17:57:47 CET Pino Toscano
wrote:
> Continuation/rework of:
> https://www.redhat.com/archives/libguestfs/2020-May/msg00020.html
> 
> This is my approach, as I explained here:
> https://bugzilla.redhat.com/show_bug.cgi?id=1828952#c4
> https://www.redhat.com/archives/libguestfs/2020-May/msg00035.html
> IOW: do not attempt to relabel if the guest is not enforcing, as it is
> either useless or may fail; few words more are in the comments of patch
> #3.
Are there any non-ideological actual technical objection to this patch
series?

If not, I'll push it in a week.

Thanks,
-- 
Pino Toscano

On Wed, Nov 11, 2020 at 12:52:31PM +0100, Pino Toscano
wrote:
> On Wednesday, 23 September 2020 17:57:47 CET Pino Toscano wrote:
> > Continuation/rework of:
> > https://www.redhat.com/archives/libguestfs/2020-May/msg00020.html
> > 
> > This is my approach, as I explained here:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1828952#c4
> > https://www.redhat.com/archives/libguestfs/2020-May/msg00035.html
> > IOW: do not attempt to relabel if the guest is not enforcing, as it is
> > either useless or may fail; few words more are in the comments of
patch
> > #3.
> 
> Are there any non-ideological actual technical objection to this patch
> series?
> 
> If not, I'll push it in a week.
Yes, I have technical objections.

I do not have any "ideological" objections to it.

Please do not push the patch as is.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
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