Re: [PATCH v2 4/4] cryptodisk: Remove unneeded found_uuid from cryptomount args

[Patrick Steinhardt]

On Mon, Sep 27, 2021 at 06:14:03PM -0500, Glenn Washburn wrote:
> The member found_uuid was never used by the crypto-backends, but was used to
> determine if a crypto-backend successfully mounted a cryptodisk with a given
> uuid. This is not needed however, because grub_device_iterate will return 1
> iff grub_cryptodisk_scan_device returns 1. And grub_cryptodisk_scan_device
> will only return 1 if a search_uuid has been specified and a cryptodisk was
> successfully setup by a crypto-backend. So the return value of
> grub_cryptodisk_scan_device is equivalent to found_uuid.

Is that always the case though? Most notably, `scan_device_real` will
only set `have_it = 1` in case we have recovered the key. If the
cryptodisk existed before and was found via `get_by_source_disk`, then
we wouldn't set `have_it` at all. This essentially means that we'd only
set `have_it` in case we found a new cryptodisk, but not if we return a
preexisting one.

I don't know whether this behaviour is something we rely on. My gut
feeling says it's rather a bug in the current code, which seems to be
confirmed by the error message in the `if (!have_it)` case, which says
"no such cryptodisk found". We did find one, but it's not a new one.

So in total I think your patch makes sense and fixes a bug, but the
description doesn't quite match reality.

Patrick

> Signed-off-by: Glenn Washburn <development@efficientek.com>
> ---
>  grub-core/disk/cryptodisk.c | 9 ++++-----
>  include/grub/cryptodisk.h   | 1 -
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
> index 5e153ee0a..033894257 100644
> --- a/grub-core/disk/cryptodisk.c
> +++ b/grub-core/disk/cryptodisk.c
> @@ -1046,8 +1046,6 @@ grub_cryptodisk_scan_device_real (const char *name,
>  
>      grub_cryptodisk_insert (dev, name, source);
>  
> -    cargs->found_uuid = 1;
> -
>      goto cleanup;
>    }
>    goto cleanup;
> @@ -1132,7 +1130,7 @@ grub_cryptodisk_scan_device (const char *name,
>    
>    if (err)
>      grub_print_error ();
> -  return (cargs->found_uuid && cargs->search_uuid) ? 1 : 0;
> +  return (!err && cargs->search_uuid) ? 1 : 0;
>  }
>  
>  static grub_err_t
> @@ -1152,6 +1150,7 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, int 
> argc, char **args)
>  
>    if (state[0].set) /* uuid */
>      {
> +      int found_uuid = 0;
>        grub_cryptodisk_t dev;
>  
>        dev = grub_cryptodisk_get_by_uuid (args[0]);
> @@ -1164,9 +1163,9 @@ grub_cmd_cryptomount (grub_extcmd_context_t ctxt, int 
> argc, char **args)
>  
>        cargs.check_boot = state[2].set;
>        cargs.search_uuid = args[0];
> -      grub_device_iterate (&grub_cryptodisk_scan_device, &cargs);
> +      found_uuid = grub_device_iterate (&grub_cryptodisk_scan_device, 
> &cargs);
>  
> -      if (!cargs.found_uuid)
> +      if (!found_uuid)
>       return grub_error (GRUB_ERR_BAD_ARGUMENT, "no such cryptodisk found");
>        return GRUB_ERR_NONE;
>      }
> diff --git a/include/grub/cryptodisk.h b/include/grub/cryptodisk.h
> index 230167ab0..f4afb9cbd 100644
> --- a/include/grub/cryptodisk.h
> +++ b/include/grub/cryptodisk.h
> @@ -70,7 +70,6 @@ typedef gcry_err_code_t
>  struct grub_cryptomount_args
>  {
>    grub_uint32_t check_boot : 1;
> -  grub_uint32_t found_uuid : 1;
>    char *search_uuid;
>    grub_uint8_t *key_data;
>    grub_size_t key_len;
> -- 
> 2.32.0
>

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