[PATCH v4 2/5] tpm: Return on tpm2_create_primary() failure in tpm2_load_null()

[Jarkko Sakkinen]

tpm2_load_null() ignores the return value of tpm2_create_primary().
Further, it does not heal from the situation when memcmp() returns zero.

Address this by returning on failure and saving the null key if there
was no detected interference in the bus.

Cc: stable at vger.kernel.org # v6.10+
Fixes: eb24c9788cd9 ("tpm: disable the TPM if NULL name changes")
Signed-off-by: Jarkko Sakkinen <jarkko at kernel.org>
---
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 | 38 +++++++++++++++++---------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 795f4c7c6adb..a62f64e21511 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -915,32 +915,34 @@ 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)
+			       &tmp_null_key);
+	if (rc != -EINVAL) {
+		if (!rc)
+			*null_key = tmp_null_key;
 		return rc;
+	}
+	dev_info(&chip->dev, "the null key has been reset\n");
 
-	/* 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 */
+	rc = tpm2_create_primary(chip, TPM2_RH_NULL, &tmp_null_key, name);
+	if (rc)
 		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");
-	chip->flags |= TPM_CHIP_FLAG_DISABLE;
 
+	/* Return the null key if the name has not been changed: */
+	if (memcmp(name, chip->null_key_name, sizeof(name)) == 0) {
+		*null_key = tmp_null_key;
+		return 0;
+	}
+
+	/* Deduce from the name change TPM interference: */
+	dev_err(&chip->dev, "the null key integrity check failedh\n");
+	tpm2_flush_context(chip, tmp_null_key);
+	chip->flags |= TPM_CHIP_FLAG_DISABLE;
 	return rc;
 }
 
-- 
2.46.0