linux-kernel - [PATCH v2] KEYS: trusted: allow module init if TPM is inactive or deactivated

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Message-ID: <20190802150733.1972-1-roberto.sassu@huawei.com>
Date:   Fri, 2 Aug 2019 17:07:33 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     <jarkko.sakkinen@...ux.intel.com>, <jejb@...ux.ibm.com>,
        <zohar@...ux.ibm.com>, <jgg@...pe.ca>, <tyhicks@...onical.com>
CC:     <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <keyrings@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <crazyt2019+lml@...il.com>, <nayna@...ux.vnet.ibm.com>,
        <silviu.vlasceanu@...wei.com>,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: [PATCH v2] KEYS: trusted: allow module init if TPM is inactive or deactivated

Commit c78719203fc6 ("KEYS: trusted: allow trusted.ko to initialize w/o a
TPM") allows the trusted module to be loaded even a TPM is not found to
avoid module dependency problems.

However, trusted module initialization can still fail if the TPM is
inactive or deactivated. This patch ignores tpm_get_random() errors in
init_digests() and returns -EFAULT in pcrlock() if the TPM didn't return
random data.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 security/keys/trusted.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/security/keys/trusted.c b/security/keys/trusted.c
index 9a94672e7adc..34f04ffcf2e5 100644
--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -389,6 +389,10 @@ static int pcrlock(const int pcrnum)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
+	/* This happens if the TPM didn't return random data */
+	if (!digests)
+		return -EFAULT;
+
 	return tpm_pcr_extend(chip, pcrnum, digests) ? -EINVAL : 0;
 }
 
@@ -1233,10 +1237,8 @@ static int __init init_digests(void)
 	int i;
 
 	ret = tpm_get_random(chip, digest, TPM_MAX_DIGEST_SIZE);
-	if (ret < 0)
-		return ret;
-	if (ret < TPM_MAX_DIGEST_SIZE)
-		return -EFAULT;
+	if (ret < 0 || ret < TPM_MAX_DIGEST_SIZE)
+		return 0;
 
 	digests = kcalloc(chip->nr_allocated_banks, sizeof(*digests),
 			  GFP_KERNEL);
-- 
2.17.1