Re: [PATCH 3/4] cryptodisk: Add options to cryptomount to support keyfiles

[Daniel Kiper]

On Fri, May 06, 2022 at 03:45:59AM -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 | 86 ++++++++++++++++++++++++++++++++++++-
>  include/grub/cryptodisk.h   |  2 +
>  include/grub/file.h         |  2 +
>  3 files changed, 89 insertions(+), 1 deletion(-)
>
> diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
> index 9f5dc7acb..19af4fa49 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 +1175,85 @@ 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 */
> +    {
> +      const char *p = NULL;
> +      grub_file_t keyfile;
> +      unsigned long long keyfile_offset = 0, keyfile_size = 0;
> +
> +      if (state[5].set) /* keyfile-offset */
> +     {
> +       keyfile_offset = grub_strtoull (state[5].arg, &p, 0);

Hmmm... Could not you use grub_strtoul() instead of grub_strtoull()?

> +
> +       if (grub_errno != GRUB_ERR_NONE)
> +         return grub_errno;

Could you explain why do you think this is needed? I think this check is
redundant. "man strtoul" says:

  If endptr is not NULL, strtoul() stores the address of the first invalid
  character in *endptr. If there were no digits at all, strtoul() stores the
  original value of nptr in *endptr (and returns 0). In particular, if *nptr
  is not '\0' but **endptr is '\0' on return, the entire string is valid.

> +       if (state[5].arg[0] == '\0' || *p != '\0')
> +         return grub_error (GRUB_ERR_BAD_ARGUMENT,
> +                            N_("non-numeric or invalid keyfile offset `%s'"),
> +                            state[5].arg);
> +     }
> +
> +      if (state[6].set) /* keyfile-size */
> +     {
> +       keyfile_size = grub_strtoul (state[6].arg, &p, 0);
> +
> +       if (state[6].arg[0] == '\0' || *p != '\0')
> +         return grub_error (GRUB_ERR_BAD_ARGUMENT,
> +                            N_("non-numeric or invalid keyfile size `%s'"),
> +                            state[6].arg);
> +
> +       if (grub_errno != GRUB_ERR_NONE)
> +         return grub_errno;

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"));
> +     }
> +
> +      keyfile = grub_file_open (state[4].arg,
> +                             GRUB_FILE_TYPE_CRYPTODISK_ENCRYPTION_KEY);
> +      if (keyfile == NULL)
> +     return grub_errno;
> +
> +      if (keyfile_offset > keyfile->size)
> +     {
> +       keyfile_offset = keyfile->size;

I do not understand this keyfile_offset clamp. Could you enlighten me?
In general I think you should fail here.

> +       grub_dprintf ("cryptodisk","Keyfile offset, %llu, is greater than"
> +                                  "keyfile size, %" PRIuGRUB_UINT64_T "\n",
> +                                  keyfile_offset, keyfile->size);

Both keyfile_offset and keyfile->size are the same here.

> +     }
> +
> +      if (grub_file_seek (keyfile, (grub_off_t) keyfile_offset) == 
> (grub_off_t) -1)
> +     return grub_errno;
> +
> +      if (keyfile_size > 0)

I think "!= 0" would be more natural here.

> +     {
> +       if (keyfile_size > (keyfile->size - keyfile_offset))
> +         return grub_error (GRUB_ERR_FILE_READ_ERROR,
> +                            N_("keyfile is too small: requested %llu bytes,"
> +                               " but the file only has %" PRIuGRUB_UINT64_T
> +                               " bytes"),
> +                            keyfile_size,
> +                            keyfile->size);

This error message is confusing. I think "keyfile->size" should be 
"keyfile->size - keyfile_offset".

> +       cargs.key_len = keyfile_size;
> +     }
> +      else
> +     cargs.key_len = keyfile->size - keyfile_offset;
> +
> +      cargs.key_data = grub_malloc (cargs.key_len);
> +      if (cargs.key_data == NULL)
> +     return GRUB_ERR_OUT_OF_MEMORY;
> +
> +      if (grub_file_read (keyfile, cargs.key_data, cargs.key_len) != 
> (grub_ssize_t) cargs.key_len)
> +     return grub_error (GRUB_ERR_FILE_READ_ERROR, (N_("reading key file")));

s/reading key file/cannot read key file/?

Daniel