[PATCH v8 2/3] tpm: Rollback tpm2_load_null()

[Jarkko Sakkinen <jarkko@xxxxxxxxxx>]

Do not continue on tpm2_create_primary() failure in tpm2_load_null().

Cc: stable@xxxxxxxxxxxxxxx # v6.10+
Fixes: eb24c9788cd9 ("tpm: disable the TPM if NULL name changes")
Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---
v8:
- Fix stray character in a log message.
v7:
- No changes.
v6:
- Address Stefan's remark:
  https://lore.kernel.org/linux-integrity/def4ec2d-584b-405f-9d5e-99267013c3c0@xxxxxxxxxxxxx/
v5:
- Fix the TPM error code leak from tpm2_load_context().
v4:
- No changes.
v3:
- Update log messages. Previously the log message incorrectly stated
  on load failure that integrity check had been failed, even tho the
  check is done *after* the load operation.
v2:
- Refined the commit message.
- Reverted tpm2_create_primary() changes. They are not required if
  tmp_null_key is used as the parameter.
---
 drivers/char/tpm/tpm2-sessions.c | 44 +++++++++++++++++---------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index a0306126e86c..950a3e48293b 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -915,33 +915,37 @@ static int tpm2_parse_start_auth_session(struct tpm2_auth *auth,
 
 static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 {
-	int rc;
 	unsigned int offset = 0; /* dummy offset for null seed context */
 	u8 name[SHA256_DIGEST_SIZE + 2];
+	u32 tmp_null_key;
+	int rc;
 
 	rc = tpm2_load_context(chip, chip->null_key_context, &offset,
-			       null_key);
-	if (rc != -EINVAL)
-		return rc;
+			       &tmp_null_key);
+	if (rc != -EINVAL) {
+		if (!rc)
+			*null_key = tmp_null_key;
+		goto err;
+	}
 
-	/* an integrity failure may mean the TPM has been reset */
-	dev_err(&chip->dev, "NULL key integrity failure!\n");
-	/* check the null name against what we know */
-	tpm2_create_primary(chip, TPM2_RH_NULL, NULL, name);
-	if (memcmp(name, chip->null_key_name, sizeof(name)) == 0)
-		/* name unchanged, assume transient integrity failure */
-		return rc;
-	/*
-	 * Fatal TPM failure: the NULL seed has actually changed, so
-	 * the TPM must have been illegally reset.  All in-kernel TPM
-	 * operations will fail because the NULL primary can't be
-	 * loaded to salt the sessions, but disable the TPM anyway so
-	 * userspace programmes can't be compromised by it.
-	 */
-	dev_err(&chip->dev, "NULL name has changed, disabling TPM due to interference\n");
+	/* Try to re-create null key, given the integrity failure: */
+	rc = tpm2_create_primary(chip, TPM2_RH_NULL, &tmp_null_key, name);
+	if (rc)
+		goto err;
+
+	/* Return null key if the name has not been changed: */
+	if (!memcmp(name, chip->null_key_name, sizeof(name))) {
+		*null_key = tmp_null_key;
+		return 0;
+	}
+
+	/* Deduce from the name change TPM interference: */
+	dev_err(&chip->dev, "null key integrity check failed\n");
+	tpm2_flush_context(chip, tmp_null_key);
 	chip->flags |= TPM_CHIP_FLAG_DISABLE;
 
-	return rc;
+err:
+	return rc ? -ENODEV : 0;
 }
 
 /**
-- 
2.47.0