[PATCH 13/14] tpm2: allow some command parameters to be NULL

[Gary Lin]

There are some parameters of TPM2 commmands allowing to be empty such
as 'encryptedSalt' of 'TPM2_StartAuthSession' and 'pcrDigest' of
'TPM2_PolicyPCR'. Instead of forcing the user of those functions to
declare an empty variable, we can just pack a u16 zero to fabricate an
empty variable when the user passes NULL for them.

This also fixes the potential crash caused by
grub_tpm2_protector_srk_recover() that invokes TPM2_PolicyPCR() with a
NULL pcrDigest.

Signed-off-by: Gary Lin <glin@suse.com>
---
 grub-core/tpm2/tpm2.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/grub-core/tpm2/tpm2.c b/grub-core/tpm2/tpm2.c
index 470fe7fc1..d67699a24 100644
--- a/grub-core/tpm2/tpm2.c
+++ b/grub-core/tpm2/tpm2.c
@@ -238,7 +238,10 @@ TPM2_StartAuthSession (const TPMI_DH_OBJECT tpmKey,
   if (tag == TPM_ST_SESSIONS)
     grub_tpm2_mu_TPMS_AUTH_COMMAND_Marshal (&in, authCommand);
   grub_tpm2_mu_TPM2B_Marshal (&in, nonceCaller->size, nonceCaller->buffer);
-  grub_tpm2_mu_TPM2B_Marshal (&in, encryptedSalt->size, encryptedSalt->secret);
+  if (encryptedSalt)
+    grub_tpm2_mu_TPM2B_Marshal (&in, encryptedSalt->size, 
encryptedSalt->secret);
+  else
+    grub_tpm2_buffer_pack_u16 (&in, 0);
   grub_tpm2_buffer_pack_u8 (&in, sessionType);
   grub_tpm2_mu_TPMT_SYM_DEF_Marshal (&in, symmetric);
   grub_tpm2_buffer_pack_u16 (&in, authHash);
@@ -295,7 +298,10 @@ TPM2_PolicyPCR (const TPMI_SH_POLICY policySessions,
   grub_tpm2_buffer_pack_u32 (&in, policySessions);
   if (tag == TPM_ST_SESSIONS)
     grub_tpm2_mu_TPMS_AUTH_COMMAND_Marshal (&in, authCommand);
-  grub_tpm2_mu_TPM2B_Marshal (&in, pcrDigest->size, pcrDigest->buffer);
+  if (pcrDigest)
+    grub_tpm2_mu_TPM2B_Marshal (&in, pcrDigest->size, pcrDigest->buffer);
+  else
+    grub_tpm2_buffer_pack_u16 (&in, 0);
   grub_tpm2_mu_TPML_PCR_SELECTION_Marshal (&in, pcrs);
   if (in.error)
     return TPM_RC_FAILURE;
-- 
2.35.3