Re: [PATCH v7 12/17] luks2: Better error handling when setting up the cryptodisk

[Glenn Washburn]

This patch got mangled accidentally with patch 5.  I'll update them
both.

Glenn

On Fri,  4 Dec 2020 10:43:41 -0600
Glenn Washburn <development@efficientek.com> wrote:

> First, check to make sure that source disk has a known size. If not,
> print debug message and return error. There are 4 cases where
> GRUB_DISK_SIZE_UNKNOWN is set (biosdisk, obdisk, ofdisk, and uboot),
> and in all those cases processing continues. So this is probably a bit
> conservative. However, 3 of the cases seem pathological, and the
> other, biosdisk, happens when booting from a cd. Since I doubt
> booting from a LUKS2 volume on a cd is a big use case, we'll error
> until someone complains.
> 
> Do some sanity checking on data coming from the luks header. If
> segment.size is "dynamic",
> 
> Check for errors from grub_strtoull when converting segment size from
> string. If a GRUB_ERR_BAD_NUMBER error was returned, then the string
> was not a valid parsable number, so skip the key. If
> GRUB_ERR_OUT_OF_RANGE was returned, then there was an overflow in
> converting to a 64-bit unsigned integer. So this could be a very
> large disk (perhaps large raid array). In this case, we want to
> continue to try to use this key so long as the source disk's size is
> greater than this segment size. Otherwise, this is an invalid
> segment, and continue on to the next key.
> 
> Signed-off-by: Glenn Washburn <development@efficientek.com>
> ---
>  grub-core/disk/luks2.c | 98
> +++++++++++++++++++++++++++++++++++++----- include/grub/disk.h    |
> 17 ++++++++ 2 files changed, 105 insertions(+), 10 deletions(-)
> 
> diff --git a/grub-core/disk/luks2.c b/grub-core/disk/luks2.c
> index de2e70796..1bb3a333d 100644
> --- a/grub-core/disk/luks2.c
> +++ b/grub-core/disk/luks2.c
> @@ -290,7 +290,7 @@ luks2_get_keyslot (grub_luks2_keyslot_t *k,
> grub_luks2_digest_t *d, grub_luks2_s break;
>      }
>    if (i == size)
> -      return grub_error (GRUB_ERR_FILE_NOT_FOUND, "No digest for
> keyslot \"%"PRIuGRUB_UINT64_T"\"", k->slot_key);
> +      return grub_error (GRUB_ERR_FILE_NOT_FOUND, "No digest for
> keyslot \"%"PRIuGRUB_UINT64_T"\"", k->json_slot_key); 
>    /* Get segment that matches the digest. */
>    if (grub_json_getvalue (&segments, root, "segments") ||
> @@ -308,7 +308,7 @@ luks2_get_keyslot (grub_luks2_keyslot_t *k,
> grub_luks2_digest_t *d, grub_luks2_s break;
>      }
>    if (i == size)
> -    return grub_error (GRUB_ERR_FILE_NOT_FOUND, "No segment for
> digest \"%"PRIuGRUB_UINT64_T"\"", d->slot_key);
> +    return grub_error (GRUB_ERR_FILE_NOT_FOUND, "No segment for
> digest \"%"PRIuGRUB_UINT64_T"\"", d->json_slot_key); 
>    return GRUB_ERR_NONE;
>  }
> @@ -600,37 +600,115 @@ luks2_recover_key (grub_disk_t source,
>        goto err;
>      }
>  
> +  if (source->total_sectors == GRUB_DISK_SIZE_UNKNOWN)
> +    {
> +      /* FIXME: Allow use of source disk, and maybe cause errors in
> read. */
> +      grub_dprintf ("luks2", "Source disk %s has an unknown size, "
> +                          "conservatively returning error\n",
> source->name);
> +      ret = grub_error (GRUB_ERR_BUG, "Unknown size of luks2 source
> device");
> +      goto err;
> +    }
> +
>    /* Try all keyslot */
>    for (i = 0; i < size; i++)
>      {
> +      typeof(source->total_sectors) max_crypt_sectors = 0;
> +
> +      grub_errno = GRUB_ERR_NONE;
>        ret = luks2_get_keyslot (&keyslot, &digest, &segment, json, i);
>        if (ret)
>       goto err;
> +      if (grub_errno != GRUB_ERR_NONE)
> +       grub_dprintf ("luks2", "Ignoring unhandled error %d from
> luks2_get_keyslot\n", grub_errno); 
>        if (keyslot.priority == 0)
>       {
> -       grub_dprintf ("luks2", "Ignoring keyslot
> \"%"PRIuGRUB_UINT64_T"\" due to priority\n", keyslot.slot_key);
> +       grub_dprintf ("luks2", "Ignoring keyslot
> \"%"PRIuGRUB_UINT64_T"\" due to priority\n", keyslot.json_slot_key);
> continue; }
>  
> -      grub_dprintf ("luks2", "Trying keyslot
> \"%"PRIuGRUB_UINT64_T"\"\n", keyslot.slot_key);
> +      grub_dprintf ("luks2", "Trying keyslot
> \"%"PRIuGRUB_UINT64_T"\"\n", keyslot.json_slot_key); 
>        /* Set up disk according to keyslot's segment. */
>        crypt->offset_sectors = grub_divmod64 (segment.offset,
> segment.sector_size, NULL); crypt->log_sector_size = sizeof (unsigned
> int) * 8
>               - __builtin_clz ((unsigned int) segment.sector_size)
> - 1;
> +      /* Set to the source disk size, which is the maximum we allow.
> */
> +      max_crypt_sectors = grub_disk_convert_sector(source,
> +
> source->total_sectors,
> +
> crypt->log_sector_size); +
> +      if (max_crypt_sectors < crypt->offset_sectors)
> +     {
> +       grub_dprintf ("luks2", "Segment \"%"PRIuGRUB_UINT64_T"\"
> has offset"
> +                              " %"PRIuGRUB_UINT64_T" which is
> greater than"
> +                              " source disk size
> %"PRIuGRUB_UINT64_T","
> +                              " skipping\n",
> +                              segment.json_slot_key,
> crypt->offset_sectors,
> +                              max_crypt_sectors);
> +       continue;
> +     }
> +
>        if (grub_strcmp (segment.size, "dynamic") == 0)
> -     crypt->total_sectors = (grub_disk_get_size (source) >>
> (crypt->log_sector_size - source->log_sector_size))
> -                            - crypt->offset_sectors;
> +     crypt->total_sectors = max_crypt_sectors -
> crypt->offset_sectors; else
> -     crypt->total_sectors = grub_strtoull (segment.size, NULL,
> 10) >> crypt->log_sector_size;
> +     {
> +       grub_errno = GRUB_ERR_NONE;
> +       /* Convert segment.size to sectors, rounding up to nearest
> sector */
> +       crypt->total_sectors = grub_strtoull (segment.size, NULL,
> 10);
> +       crypt->total_sectors = ALIGN_UP (crypt->total_sectors,
> +                                        1 <<
> crypt->log_sector_size);
> +       crypt->total_sectors >>= crypt->log_sector_size;
> +
> +       if (grub_errno == GRUB_ERR_NONE)
> +         ;
> +       else if (grub_errno == GRUB_ERR_BAD_NUMBER)
> +         {
> +           grub_dprintf ("luks2", "Segment
> \"%"PRIuGRUB_UINT64_T"\" size"
> +                                  " \"%s\" is not a parsable
> number\n",
> +                                  segment.json_slot_key,
> segment.size);
> +           continue;
> +         }
> +       else if (grub_errno == GRUB_ERR_OUT_OF_RANGE)
> +         {
> +           /*
> +            * There was an overflow in parsing segment.size, so
> disk must
> +            * be very large or the string is incorrect.
> +            */
> +           grub_dprintf ("luks2", "Segment
> \"%"PRIuGRUB_UINT64_T"\" size"
> +                                  " %s overflowed 64-bit unsigned
> integer,"
> +                                  " the end of the crypto device
> will be"
> +                                  " inaccessible\n",
> +                                  segment.json_slot_key,
> segment.size);
> +           if (crypt->total_sectors > max_crypt_sectors)
> +             crypt->total_sectors = max_crypt_sectors;
> +         }
> +     }
> +
> +      if (crypt->total_sectors == 0)
> +     {
> +       grub_dprintf ("luks2", "Segment \"%"PRIuGRUB_UINT64_T"\"
> has zero"
> +                              " sectors, skipping\n",
> +                              segment.json_slot_key);
> +       continue;
> +     }
> +      else if (max_crypt_sectors < (crypt->offset_sectors +
> crypt->total_sectors))
> +     {
> +       grub_dprintf ("luks2", "Segment \"%"PRIuGRUB_UINT64_T"\"
> has last"
> +                              " data position greater than source
> disk size,"
> +                              " the end of the crypto device will
> be"
> +                              " inaccessible\n",
> +                              segment.json_slot_key);
> +       /* Allow decryption up to the end of the source disk. */
> +       crypt->total_sectors = max_crypt_sectors -
> crypt->offset_sectors;
> +     }
>  
>        ret = luks2_decrypt_key (candidate_key, source, crypt,
> &keyslot, (const grub_uint8_t *) passphrase, grub_strlen
> (passphrase)); if (ret)
>       {
>         grub_dprintf ("luks2", "Decryption with keyslot
> \"%"PRIuGRUB_UINT64_T"\" failed: %s\n",
> -                     keyslot.slot_key, grub_errmsg);
> +                     keyslot.json_slot_key, grub_errmsg);
>         continue;
>       }
>  
> @@ -638,7 +716,7 @@ luks2_recover_key (grub_disk_t source,
>        if (ret)
>       {
>         grub_dprintf ("luks2", "Could not open keyslot
> \"%"PRIuGRUB_UINT64_T"\": %s\n",
> -                     keyslot.slot_key, grub_errmsg);
> +                     keyslot.json_slot_key, grub_errmsg);
>         continue;
>       }
>  
> @@ -646,7 +724,7 @@ luks2_recover_key (grub_disk_t source,
>         * TRANSLATORS: It's a cryptographic key slot: one element of
> an array
>         * where each element is either empty or holds a key.
>         */
> -      grub_printf_ (N_("Slot \"%"PRIuGRUB_UINT64_T"\" opened\n"),
> keyslot.slot_key);
> +      grub_printf_ (N_("Slot \"%"PRIuGRUB_UINT64_T"\" opened\n"),
> keyslot.json_slot_key); 
>        candidate_key_len = keyslot.key_size;
>        break;
> diff --git a/include/grub/disk.h b/include/grub/disk.h
> index 0fb727d3d..f9227f285 100644
> --- a/include/grub/disk.h
> +++ b/include/grub/disk.h
> @@ -27,6 +27,8 @@
>  #include <grub/device.h>
>  /* For NULL.  */
>  #include <grub/mm.h>
> +/* For ALIGN_UP.  */
> +#include <grub/misc.h>
>  
>  /* These are used to set a device id. When you add a new disk device,
>     you must define a new id for it here.  */
> @@ -174,6 +176,21 @@ typedef struct grub_disk_memberlist
> *grub_disk_memberlist_t; /* Return value of
> grub_disk_native_sectors() in case disk size is unknown. */ #define
> GRUB_DISK_SIZE_UNKNOWN         0xffffffffffffffffULL 
> +/* Convert sector number from disk sized sectors to a log-size sized
> sector. */ +static inline grub_disk_addr_t
> +grub_disk_convert_sector (grub_disk_t disk,
> +                       grub_disk_addr_t sector,
> +                       grub_size_t log_sector_size)
> +{
> +  if (disk->log_sector_size < log_sector_size)
> +    {
> +      sector = ALIGN_UP (sector, 1 << (log_sector_size /
> disk->log_sector_size));
> +      return sector >> (log_sector_size - disk->log_sector_size);
> +    }
> +  else
> +    return sector << (disk->log_sector_size - log_sector_size);
> +}
> +
>  /* Convert to GRUB native disk sized sector from disk sized sector.
> */ static inline grub_disk_addr_t
>  grub_disk_from_native_sector (grub_disk_t disk, grub_disk_addr_t
> sector)