Re: [PATCH v2 3/5] cryptodisk: Add options to cryptomount to support keyfiles

[Daniel Kiper]

On Fri, May 13, 2022 at 12:00:49PM -0500, Glenn Washburn wrote:
> From: John Lane <john@lane.uk.net>
>
> Add the options --key-file, --keyfile-offset, and --keyfile-size to
> cryptomount and code to put read the requested key file data and pass
> via the cargs struct. Note, key file data is for all intents and purposes
> equivalent to a password given to cryptomount. So there is no need to
> enable support for key files in the various crypto backends (eg. LUKS1)
> because the key data is passed just as if it were a password.
>
> Signed-off-by: John Lane <john@lane.uk.net>
> GNUtoo@cyberdimension.org: rebase, patch split, small fixes, commit message
> Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
> development@efficientek.com: rebase and rework to use cryptomount arg passing,
>   minor fixes, improve commit message
> Signed-off-by: Glenn Washburn <development@efficientek.com>
> ---
>  grub-core/disk/cryptodisk.c | 104 +++++++++++++++++++++++++++++++++++-
>  include/grub/cryptodisk.h   |   2 +
>  include/grub/file.h         |   2 +
>  3 files changed, 107 insertions(+), 1 deletion(-)
>
> diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
> index 9f5dc7acb..94640b502 100644
> --- a/grub-core/disk/cryptodisk.c
> +++ b/grub-core/disk/cryptodisk.c
> @@ -42,6 +42,9 @@ static const struct grub_arg_option options[] =
>      {"all", 'a', 0, N_("Mount all."), 0, 0},
>      {"boot", 'b', 0, N_("Mount all volumes with `boot' flag set."), 0, 0},
>      {"password", 'p', 0, N_("Password to open volumes."), 0, 
> ARG_TYPE_STRING},
> +    {"key-file", 'k', 0, N_("Key file"), 0, ARG_TYPE_STRING},
> +    {"keyfile-offset", 'O', 0, N_("Key file offset (bytes)"), 0, 
> ARG_TYPE_INT},
> +    {"keyfile-size", 'S', 0, N_("Key file data size (bytes)"), 0, 
> ARG_TYPE_INT},
>      {0, 0, 0, 0, 0, 0}
>    };
>
> @@ -1172,6 +1175,103 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, int 
> argc, char **args)
>        cargs.key_len = grub_strlen (state[3].arg);
>      }
>
> +  if (state[4].set) /* keyfile */
> +    {
> +      char tmp_errmsg[GRUB_MAX_ERRMSG];
> +      const char *p = NULL;
> +      grub_file_t keyfile;
> +      unsigned long long keyfile_offset = 0, keyfile_size = 0;
> +
> +      if (state[5].set) /* keyfile-offset */
> +     {
> +       grub_errno = GRUB_ERR_NONE;
> +       keyfile_offset = grub_strtoull (state[5].arg, &p, 0);
> +
> +       if (state[5].arg[0] == '\0' || *p != '\0')
> +         {
> +           if (grub_errno != GRUB_ERR_NONE)
> +             {
> +               grub_strncpy (tmp_errmsg, grub_errmsg, GRUB_MAX_ERRMSG);
> +               return grub_error (grub_errno,
> +                                  N_("non-numeric or invalid keyfile offset 
> `%s': %s"),
> +                                  state[5].arg, tmp_errmsg);
> +             }
> +           else
> +             return grub_error (GRUB_ERR_BAD_ARGUMENT,
> +                                N_("invalid keyfile offset `%s': non-numeric"
> +                                   " characters at end of number"),
> +                                state[5].arg);

I think this does not give us a lot of value. I would just do

   if (state[5].arg[0] == '\0' || *p != '\0')
     return grub_error (GRUB_ERR_BAD_NUMBER, ...

> +         }
> +     }
> +
> +      if (state[6].set) /* keyfile-size */
> +     {
> +       grub_errno = GRUB_ERR_NONE;
> +       keyfile_size = grub_strtoull (state[6].arg, &p, 0);
> +
> +       if (state[6].arg[0] == '\0' || *p != '\0')
> +         {
> +           if (grub_errno != GRUB_ERR_NONE)
> +             {
> +               grub_strncpy (tmp_errmsg, grub_errmsg, GRUB_MAX_ERRMSG);
> +               return grub_error (grub_errno,
> +                                  N_("non-numeric or invalid keyfile offset 
> `%s': %s"),
> +                                  state[5].arg, tmp_errmsg);
> +             }
> +           else
> +             return grub_error (GRUB_ERR_BAD_ARGUMENT,
> +                                N_("invalid keyfile offset `%s': non-numeric"
> +                                   " characters at end of number"),
> +                                state[6].arg);

Ditto.

> +         }
> +
> +       if (keyfile_size > GRUB_CRYPTODISK_MAX_KEYFILE_SIZE)
> +         return grub_error (GRUB_ERR_OUT_OF_RANGE,
> +                            N_("key file size exceeds maximum (%d)"),
> +                            GRUB_CRYPTODISK_MAX_KEYFILE_SIZE);
> +
> +       if (keyfile_size == 0)
> +         return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("key file size is 0"));

Nit, I would move this before the "if (keyfile_size > ...". This would
be more natural.

Daniel