[Libguestfs] [libguestfs-common PATCH 04/12] mltools/tools_utils: allow multiple "--key" options for OCaml tools too

[Laszlo Ersek]

Commit c10c8baedb88 ("options: Allow multiple --key parameters.",
2019-11-28) enabled multi-key support for the C-language tools only.
C-language tools parse the "--key" option as follows:

  OPTION_key                      [options/options.h]
    key_store_add_from_selector() [options/keys.c]
      key_store_import_key()      [options/keys.c]

And the last function above simply appends the imported key to the
keystore.

However, commit c10c8baedb88 was ineffective (already at the time of
writing) for OCaml-language tools. From commit f84d95474ccf ("Introduce a
--key option in tools that accept keys", 2018-09-21), OCaml tools first
de-duplicate the "--key" options (using the device identifier as a hash
table key), and only (distinct) elements of the flattened hash table are
passed to key_store_import_key():

  parse_key_selector                    [mltools/tools_utils.ml]
    Hashtbl.replace

  inspect_decrypt                       [mltools/tools_utils.ml]
    Hashtbl.fold
    c_inspect_decrypt                   [mltools/tools_utils.ml]
      guestfs_int_mllib_inspect_decrypt [mltools/tools_utils-c.c]
        key_store_import_key()          [options/keys.c]

This problem can be demonstrated by passing two keys, a good one and a
wrong one, for the same device identifier, to a C-language guestfs tool
(such as virt-cat), and to an OCaml-language one (such as
virt-get-kernel). The latter is sensitive to the order of "--key" options:

$ virt-cat \
    --key /dev/sda2:key:good-key \
    --key /dev/sda2:key:wrong-key \
    -d DOMAIN \
    /no-such-file
> libguestfs: error: download: /no-such-file: No such file or directory

Here the wrong key (passed as the 2nd "--key" option) does not invalidate
the first (good) key.

$ virt-get-kernel \
    --key /dev/sda2:key:good-key \
    --key /dev/sda2:key:wrong-key \
    -d DOMAIN \
    -o /tmp
> virt-get-kernel: could not find key to open LUKS encrypted /dev/sda2.
>
> Try using --key on the command line.
>
> Original error: cryptsetup_open: cryptsetup exited with status 2: No key
> available with this passphrase. (0)

Here the wrong key replaces the good key.

$ virt-get-kernel \
    --key /dev/sda2:key:wrong-key \
    --key /dev/sda2:key:good-key \
    -d DOMAIN \
    -o /tmp
> download: /boot/vmlinuz-[...] -> /tmp/vmlinuz-[...]
> download: /boot/initramfs-[...].img -> /tmp/initramfs-[...].img

Reversing the order of "--key" options for the OCaml-language tool allows
the good key to prevail (and the wrong to be overwritten).

Fix this discrepancy by replacing the hash table with a plain list
(reference).

(Side comment: the hash table-based deduplication didn't do its job
entirely, either. We could still pass two keys for the same LUKS block
device: once by pathname, and another time by LUKS UUID.)

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1809453
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 mltools/tools_utils.ml | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/mltools/tools_utils.ml b/mltools/tools_utils.ml
index 8508534e16ee..6006ab7e4f6c 100644
--- a/mltools/tools_utils.ml
+++ b/mltools/tools_utils.ml
@@ -27,11 +27,11 @@ open Getopt.OptionName
  * messages.
  *)
 let prog = ref prog
 
 type key_store = {
-  keys : (string, key_store_key) Hashtbl.t;
+  keys : (string * key_store_key) list ref;
 }
 and key_store_key =
   | KeyString of string
   | KeyFileName of string
 
@@ -374,11 +374,11 @@ let create_standard_options argspec ?anon_fun ?(key_opts = false)
       | n ->
         error (f_"invalid output for --machine-readable: %s") fmt
       )
   in
   let ks = {
-    keys = Hashtbl.create 13;
+    keys = ref [];
   } in
   let argspec = ref argspec in
   let add_argspec = List.push_back argspec in
 
   add_argspec ([ S 'V'; L"version" ], Getopt.Unit print_version_and_exit, s_"Display version and exit");
@@ -393,13 +393,13 @@ let create_standard_options argspec ?anon_fun ?(key_opts = false)
   if key_opts then (
     let parse_key_selector arg =
       let parts = String.nsplit ~max:3 ":" arg in
       match parts with
       | [ device; "key"; key ] ->
-         Hashtbl.replace ks.keys device (KeyString key)
+         List.push_back ks.keys (device, KeyString key)
       | [ device; "file"; file ] ->
-         Hashtbl.replace ks.keys device (KeyFileName file)
+         List.push_back ks.keys (device, KeyFileName file)
       | _ ->
          error (f_"invalid selector string for --key: %s") arg
     in
 
     add_argspec ([ L"echo-keys" ],       Getopt.Unit c_set_echo_keys,       s_"Don’t turn off echo for passphrases");
@@ -680,24 +680,17 @@ let is_btrfs_subvolume g fs =
   with Guestfs.Error msg as exn ->
     if g#last_errno () = Guestfs.Errno.errno_EINVAL then false
     else raise exn
 
 let inspect_decrypt g ks =
-  (* Turn the keys in the key_store into a simpler struct, so it is possible
-   * to read it using the C API.
-   *)
-  let keys_as_list = Hashtbl.fold (
-    fun k v acc ->
-      (k, v) :: acc
-  ) ks.keys [] in
   (* Note we pass original 'g' even though it is not used by the
    * callee.  This is so that 'g' is kept as a root on the stack, and
    * so cannot be garbage collected while we are in the c_inspect_decrypt
    * function.
    *)
   c_inspect_decrypt g#ocaml_handle (Guestfs.c_pointer g#ocaml_handle)
-    keys_as_list
+    !(ks.keys)
 
 let with_timeout op timeout ?(sleep = 2) fn =
   let start_t = Unix.gettimeofday () in
   let rec loop () =
     if Unix.gettimeofday () -. start_t > float_of_int timeout then
-- 
2.19.1.3.g30247aa5d201