On 10/21/24 1:39 AM, Jarkko Sakkinen wrote:
tpm2_load_null() has weak and broken error handling:
- The return value of tpm2_create_primary() is ignored.
- Leaks TPM return codes from tpm2_load_context() to the caller.
- If the key name comparison succeeds returns previous error
instead of zero to the caller.
Implement a proper error rollback.
Cc: [email protected] # v6.10+
Fixes: eb24c9788cd9 ("tpm: disable the TPM if NULL name changes")
Signed-off-by: Jarkko Sakkinen <[email protected]>
--
v6:
- Address Stefan's remark:
https://lore.kernel.org/linux-integrity/[email protected]/
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 | 43 +++++++++++++++++---------------
1 file changed, 23 insertions(+), 20 deletions(-)
diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 1e12e0b2492e..bdac11964b55 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -915,33 +915,36 @@ 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");
+ rc = tpm2_create_primary(chip, TPM2_RH_NULL, &tmp_null_key, name);
+ if (rc)
+ goto err;
+
+ /* 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");
stray 'h': s/failedh/failed
+ tpm2_flush_context(chip, tmp_null_key);
chip->flags |= TPM_CHIP_FLAG_DISABLE;
- return rc;
+err:
+ return rc ? -ENODEV : 0;
}
/**
Reviewed-by: Stefan Berger <[email protected]>
