[PATCH v3] disk/cryptodisk: When cheatmounting, use the sector info of the cheat device

[Fabian Vogt <fvogt@suse.de>]

When using grub-probe with cryptodisk, the mapped block device from the host
is used directly instead of decrypting the source device in GRUB code.
In that case, the sector size and count of the host device needs to be used.
This is especially important when using luks2, which does not assign
total_sectors and log_sector_size when scanning, but only later when the
segments in the JSON area are evaluated. With an unset log_sector_size,
grub_open_device complains.

This fixes grub-probe failing with
"error: sector sizes of 1 bytes aren't supported yet."

Signed-off-by: Fabian Vogt <fvogt@suse.de>
---
v2: Moved new code from grub_cryptodisk_cheat_mount to grub_cryptodisk_open,
    which allowed to simplify the code a bit. Also improved error handling.
v3: More liberal placement of variable declarations.

 grub-core/disk/cryptodisk.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/grub-core/disk/cryptodisk.c b/grub-core/disk/cryptodisk.c
index c80cf9907..b3c76ef57 100644
--- a/grub-core/disk/cryptodisk.c
+++ b/grub-core/disk/cryptodisk.c
@@ -709,16 +709,31 @@ grub_cryptodisk_open (const char *name, grub_disk_t disk)
   if (!dev)
     return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "No such device");
 
-  disk->log_sector_size = dev->log_sector_size;
-
 #ifdef GRUB_UTIL
   if (dev->cheat)
     {
+      grub_uint64_t cheat_dev_size;
+      unsigned int cheat_log_sector_size;
+
       if (!GRUB_UTIL_FD_IS_VALID (dev->cheat_fd))
 	dev->cheat_fd = grub_util_fd_open (dev->cheat, GRUB_UTIL_FD_O_RDONLY);
       if (!GRUB_UTIL_FD_IS_VALID (dev->cheat_fd))
 	return grub_error (GRUB_ERR_IO, N_("cannot open `%s': %s"),
 			   dev->cheat, grub_util_fd_strerror ());
+
+      /* Use the sector size and count of the cheat device */
+      cheat_dev_size = grub_util_get_fd_size (dev->cheat_fd, dev->cheat, &cheat_log_sector_size);
+      if (cheat_dev_size == -1)
+        {
+          const char *errmsg = grub_util_fd_strerror ();
+          grub_util_fd_close (dev->cheat_fd);
+          dev->cheat_fd = GRUB_UTIL_FD_INVALID;
+          return grub_error (GRUB_ERR_IO, N_("failed to query size of device `%s': %s"),
+                             dev->cheat, errmsg);
+        }
+
+      dev->log_sector_size = cheat_log_sector_size;
+      dev->total_sectors = cheat_dev_size >> cheat_log_sector_size;
     }
 #endif
 
@@ -732,6 +747,7 @@ grub_cryptodisk_open (const char *name, grub_disk_t disk)
     }
 
   disk->data = dev;
+  disk->log_sector_size = dev->log_sector_size;
   disk->total_sectors = dev->total_sectors;
   disk->max_agglomerate = GRUB_DISK_MAX_MAX_AGGLOMERATE;
   disk->id = dev->id;
-- 
2.36.1