[PATCH v3 06/10] tpm2_key_protector: Unseal key from a buffer

[Gary Lin]

Extract the logic to handle the file buffer from the SRK recover
function to prepare to load the sealed key from the NV index handle.
The SRK recover function now only reads the file and sends the file
buffer to the new function. Besides this, the file format is detected
automatically before unmarshalling the data, so there is no need to use
the command option to specify the file format anymore. In other words,
'--tpm2key' and '--keyfile' are the same now.

Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
---
 .../commands/tpm2_key_protector/module.c      | 122 +++++++++++++-----
 1 file changed, 89 insertions(+), 33 deletions(-)

diff --git a/grub-core/commands/tpm2_key_protector/module.c 
b/grub-core/commands/tpm2_key_protector/module.c
index 0a5d81e4c..795f61518 100644
--- a/grub-core/commands/tpm2_key_protector/module.c
+++ b/grub-core/commands/tpm2_key_protector/module.c
@@ -218,10 +218,51 @@ tpm2_protector_srk_read_file (const char *filepath, void 
**buffer, grub_size_t *
   return err;
 }
 
+/* Check if the data is in TPM 2.0 Key File format */
+static bool
+tpm2_protector_is_tpm2key (grub_uint8_t *buffer, grub_size_t buffer_size)
+{
+  /* id-sealedkey OID (2.23.133.10.1.5) in DER */
+  const grub_uint8_t sealed_key_oid[] = {0x06, 0x06, 0x67, 0x81, 0x05, 0x0a};
+  grub_size_t skip = 0;
+
+  /* Need at least the first two bytes to check the tag and the length */
+  if (buffer_size < 2)
+    return false;
+
+  /* The first byte is always 0x30 (SEQUENCE). */
+  if (buffer[0] != 0x30)
+    return false;
+
+  /*
+   * Get the bytes of the length
+   *
+   * If the bit 8 of the second byte is 0, it is in the short form, so the 
second byte
+   * alone represents the length. Thus, the first two bytes are skipped.
+   *
+   * Otherwise, it is in the long form, and bits 1~7 indicate how many more 
bytes are in
+   * the length field, so we skip the first two bytes plus the bytes for the 
length.
+   */
+  if ((buffer[1] & 0x80) == 0)
+    skip = 2;
+  else
+    skip = (buffer[1] & 0x7F) + 2;
+
+  /* Make sure the buffer is large enough to contain id-sealedkey OID */
+  if (buffer_size < skip + sizeof (sealed_key_oid))
+    return false;
+
+  /* Check id-sealedkey OID */
+  if (grub_memcmp (buffer + skip, sealed_key_oid, sizeof (sealed_key_oid)) != 
0)
+    return false;
+
+  return true;
+}
+
 static grub_err_t
-tpm2_protector_srk_unmarshal_keyfile (void *sealed_key,
-                                     grub_size_t sealed_key_size,
-                                     tpm2_sealed_key_t *sk)
+tpm2_protector_unmarshal_raw (void *sealed_key,
+                             grub_size_t sealed_key_size,
+                             tpm2_sealed_key_t *sk)
 {
   struct grub_tpm2_buffer buf;
 
@@ -242,13 +283,13 @@ tpm2_protector_srk_unmarshal_keyfile (void *sealed_key,
 }
 
 static grub_err_t
-tpm2_protector_srk_unmarshal_tpm2key (void *sealed_key,
-                                     grub_size_t sealed_key_size,
-                                     tpm2key_policy_t *policy_seq,
-                                     tpm2key_authpolicy_t *authpol_seq,
-                                     grub_uint8_t *rsaparent,
-                                     grub_uint32_t *parent,
-                                     tpm2_sealed_key_t *sk)
+tpm2_protector_unmarshal_tpm2key (void *sealed_key,
+                                 grub_size_t sealed_key_size,
+                                 tpm2key_policy_t *policy_seq,
+                                 tpm2key_authpolicy_t *authpol_seq,
+                                 grub_uint8_t *rsaparent,
+                                 grub_uint32_t *parent,
+                                 tpm2_sealed_key_t *sk)
 {
   asn1_node tpm2key = NULL;
   grub_uint8_t rsaparent_tmp;
@@ -942,12 +983,11 @@ tpm2_protector_dump_pcr (const TPM_ALG_ID_t bank)
 }
 
 static grub_err_t
-tpm2_protector_srk_recover (const tpm2_protector_context_t *ctx,
-                           grub_uint8_t **key, grub_size_t *key_size)
+tpm2_protector_key_from_buffer (const tpm2_protector_context_t *ctx,
+                               void *buffer, grub_size_t buf_size,
+                               grub_uint8_t **key, grub_size_t *key_size)
 {
   tpm2_sealed_key_t sealed_key = {0};
-  void *file_bytes = NULL;
-  grub_size_t file_size = 0;
   grub_uint8_t rsaparent = 0;
   TPM_HANDLE_t parent_handle = 0;
   TPM_HANDLE_t srk_handle = 0;
@@ -960,22 +1000,17 @@ tpm2_protector_srk_recover (const 
tpm2_protector_context_t *ctx,
 
   /*
    * Retrieve sealed key, parent handle, policy sequence, and authpolicy
-   * sequence from the key file
+   * sequence from the buffer
   */
-  if (ctx->tpm2key != NULL)
+  if (tpm2_protector_is_tpm2key (buffer, buf_size) == true)
     {
-      err = tpm2_protector_srk_read_file (ctx->tpm2key, &file_bytes,
-                                              &file_size);
-      if (err != GRUB_ERR_NONE)
-       return err;
-
-      err = tpm2_protector_srk_unmarshal_tpm2key (file_bytes,
-                                                 file_size,
-                                                 &policy_seq,
-                                                 &authpol_seq,
-                                                 &rsaparent,
-                                                 &parent_handle,
-                                                 &sealed_key);
+      err = tpm2_protector_unmarshal_tpm2key (buffer,
+                                             buf_size,
+                                             &policy_seq,
+                                             &authpol_seq,
+                                             &rsaparent,
+                                             &parent_handle,
+                                             &sealed_key);
       if (err != GRUB_ERR_NONE)
        goto exit1;
 
@@ -991,12 +1026,8 @@ tpm2_protector_srk_recover (const 
tpm2_protector_context_t *ctx,
     }
   else
     {
-      err = tpm2_protector_srk_read_file (ctx->keyfile, &file_bytes, 
&file_size);
-      if (err != GRUB_ERR_NONE)
-       return err;
-
       parent_handle = TPM_RH_OWNER;
-      err = tpm2_protector_srk_unmarshal_keyfile (file_bytes, file_size, 
&sealed_key);
+      err = tpm2_protector_unmarshal_raw (buffer, buf_size, &sealed_key);
       if (err != GRUB_ERR_NONE)
        goto exit1;
     }
@@ -1072,6 +1103,31 @@ tpm2_protector_srk_recover (const 
tpm2_protector_context_t *ctx,
  exit1:
   grub_tpm2key_free_policy_seq (policy_seq);
   grub_tpm2key_free_authpolicy_seq (authpol_seq);
+  return err;
+}
+
+static grub_err_t
+tpm2_protector_srk_recover (const tpm2_protector_context_t *ctx,
+                           grub_uint8_t **key, grub_size_t *key_size)
+{
+  const char *filepath;
+  void *file_bytes = NULL;
+  grub_size_t file_size = 0;
+  grub_err_t err;
+
+  if (ctx->tpm2key != NULL)
+    filepath = ctx->tpm2key;
+  else if (ctx->keyfile != NULL)
+    filepath = ctx->keyfile;
+  else
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("key file not specified"));
+
+  err = tpm2_protector_srk_read_file (filepath, &file_bytes, &file_size);
+  if (err != GRUB_ERR_NONE)
+    return err;
+
+  err = tpm2_protector_key_from_buffer (ctx, file_bytes, file_size, key, 
key_size);
+
   grub_free (file_bytes);
   return err;
 }
-- 
2.43.0