[PATCH v2 2/2] devmapper/getroot: Set up cheated LUKS2 cryptodisk mount from DM parameters

[Josselin Poiret <dev@jpoiret.xyz>]

This lets a LUKS2 cryptodisk have all the cipher, hash, and sizes
filled out, otherwise they wouldn't be initialized if cheat mounted.
---
 grub-core/osdep/devmapper/getroot.c | 99 ++++++++++++++++++++++++++++-
 1 file changed, 98 insertions(+), 1 deletion(-)

diff --git a/grub-core/osdep/devmapper/getroot.c b/grub-core/osdep/devmapper/getroot.c
index ad1daf9c8..4b3458639 100644
--- a/grub-core/osdep/devmapper/getroot.c
+++ b/grub-core/osdep/devmapper/getroot.c
@@ -51,6 +51,8 @@
 #include <grub/emu/misc.h>
 #include <grub/emu/hostdisk.h>
 
+#include <grub/cryptodisk.h>
+
 static int
 grub_util_open_dm (const char *os_dev, struct dm_tree **tree,
 		   struct dm_tree_node **node)
@@ -183,7 +185,6 @@ grub_util_pull_devmapper (const char *os_dev)
       && lastsubdev)
     {
       char *grdev = grub_util_get_grub_dev (lastsubdev);
-      dm_tree_free (tree);
       if (grdev)
 	{
 	  grub_err_t err;
@@ -191,7 +192,103 @@ grub_util_pull_devmapper (const char *os_dev)
 	  if (err)
 	    grub_util_error (_("can't mount encrypted volume `%s': %s"),
 			     lastsubdev, grub_errmsg);
+          if (strncmp (uuid, "CRYPT-LUKS2-", sizeof ("CRYPT-LUKS2-") - 1) == 0)
+            {
+              /* set LUKS2 cipher and size from dm parameter, since it is not
+               * possible to determine the correct ones without unlocking, as
+               * there might be multiple segments.
+               */
+              grub_disk_t source = grub_disk_open (grdev);
+              grub_cryptodisk_t cryptodisk = grub_cryptodisk_get_by_source_disk (source);
+              grub_disk_close (source);
+              grub_addr_t start, length;
+              char *target_type = NULL;
+              char *params;
+              const char *name = dm_tree_node_get_name (node);
+              char *cipher, *cipher_mode;
+              struct dm_task *dmt;
+              grub_util_info ("populating parameters of cryptomount `%s' from DM device `%s'",
+                              uuid, name);
+              if (!(dmt = dm_task_create (DM_DEVICE_TABLE)))
+                grub_util_error (_("can't create dm task DM_DEVICE_TABLE"));
+              if (!dm_task_set_name (dmt, name))
+                grub_util_error (_("can't set dm task name to `%s'"), name);
+              if (!dm_task_run (dmt))
+                grub_util_error (_("can't run dm task for `%s'"), name);
+              dm_get_next_target (dmt, NULL, &start, &length,
+                                  &target_type, &params);
+              if (strncmp (target_type, "crypt", sizeof ("crypt")) != 0)
+                grub_util_error (_("dm target is not `crypt'"));
+
+              cryptodisk->total_sectors = length;
+              cryptodisk->log_sector_size = 9; /* default dm sector size */
+
+              /* dm target parameters for dm-crypt is
+               * <cipher> <key> <iv_offset> <device path> <offset> [<#opt_params> <opt_params>]
+               */
+              char *seek_head, *c;
+              c = params;
+
+              /* first, get the cipher name from the cipher */
+              if (!(seek_head = grub_memchr (c, '-', grub_strlen (c))))
+                grub_util_error (_("can't get cipher from dm-crypt parameters `%s'"),
+                                 params);
+              cipher = grub_strndup (c, seek_head - c);
+              c = seek_head + 1;
+
+              /* now, the cipher mode */
+              if (!(seek_head = grub_memchr (c, ' ', grub_strlen (c))))
+                grub_util_error (_("can't get cipher mode from dm-crypt parameters `%s'"),
+                                 params);
+              cipher_mode = grub_strndup (c, seek_head - c);
+
+              grub_cryptodisk_setcipher (cryptodisk, cipher, cipher_mode);
+
+              /* This is the only hash usable by PBKDF2, so set it as such */
+              cryptodisk->hash = grub_crypto_lookup_md_by_name ("sha256");
+
+              /* drop key, iv_offset, device path and offset */
+              for (int dropped_tokens = 0; dropped_tokens < 4; dropped_tokens++)
+                {
+                  seek_head++;
+                  seek_head = grub_memchr (seek_head, ' ', grub_strlen (seek_head));
+                }
+
+              /* if we have optional parameters, skip #opt_params */
+              if (seek_head && (seek_head = grub_memchr (seek_head, ' ', grub_strlen (seek_head))))
+                {
+                  seek_head++;
+                  for (;seek_head;seek_head = grub_memchr (seek_head, ' ', grub_strlen (seek_head)))
+                    {
+                      seek_head++;
+                      if (strncmp (seek_head, "sector_size:", sizeof ("sector_size:") - 1) == 0)
+                        {
+                          char *sector_size_str;
+                          unsigned long long sector_size;
+                          c = seek_head + sizeof ("sector_size:") - 1;
+                          seek_head = grub_memchr (c, ' ', grub_strlen (c));
+                          if (seek_head)
+                            sector_size_str = grub_strndup (c, seek_head - c);
+                          else
+                            sector_size_str = c;
+                          sector_size = grub_strtoull (sector_size_str, NULL, 10);
+
+                          if (sector_size != 512 && sector_size != 1024 &&
+                              sector_size != 2048 && sector_size != 4096)
+                            grub_util_error (_("dm-crypt parameter sector_size `%s' is not a valid LUKS2 sector size"),
+                                             sector_size_str);
+                          cryptodisk->log_sector_size = grub_log2ull (sector_size);
+                          grub_util_info ("set sector_size for dm `%s' to `%d'",
+                                          name, 1 << cryptodisk->log_sector_size);
+                          break;
+                        }
+                    }
+                }
+
+              dm_task_destroy (dmt);
+            }
 	}
+      dm_tree_free (tree);
       grub_free (grdev);
     }
   else
-- 
2.34.0