[PATCH v2 1/3] KEYS: trusted: Fix incorrect handling of tpm_get_random()

[Jarkko Sakkinen]

When tpm_get_random() was introduced, it defined the following API for the
return value:

1. A positive value tells how many bytes of random data was generated.
2. A negative value on error.

However, in the call sites the API was used incorrectly, i.e. as it would
only return negative values and otherwise zero. Returning he positive read
counts to the user space does not make any possible sense.

Fix this by returning -EIO when tpm_get_random() returns a positive value.

Fixes: 41ab999c80f1 ("tpm: Move tpm_get_random api into the TPM device driver")
Cc: stable at vger.kernel.org
Cc: Mimi Zohar <zohar at linux.ibm.com>
Cc: "James E.J. Bottomley" <James.Bottomley at HansenPartnership.com>
Cc: David Howells <dhowells at redhat.com>
Cc: Kent Yoder <key at linux.vnet.ibm.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen at linux.intel.com>
---
 security/keys/trusted-keys/trusted_tpm1.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index b9fe02e5f84f..c7b1701cdac5 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -403,9 +403,12 @@ static int osap(struct tpm_buf *tb, struct osapsess *s,
 	int ret;
 
 	ret = tpm_get_random(chip, ononce, TPM_NONCE_SIZE);
-	if (ret != TPM_NONCE_SIZE)
+	if (ret < 0)
 		return ret;
 
+	if (ret != TPM_NONCE_SIZE)
+		return -EIO;
+
 	tpm_buf_reset(tb, TPM_TAG_RQU_COMMAND, TPM_ORD_OSAP);
 	tpm_buf_append_u16(tb, type);
 	tpm_buf_append_u32(tb, handle);
@@ -496,8 +499,12 @@ static int tpm_seal(struct tpm_buf *tb, uint16_t keytype,
 		goto out;
 
 	ret = tpm_get_random(chip, td->nonceodd, TPM_NONCE_SIZE);
+	if (ret < 0)
+		return ret;
+
 	if (ret != TPM_NONCE_SIZE)
-		goto out;
+		return -EIO;
+
 	ordinal = htonl(TPM_ORD_SEAL);
 	datsize = htonl(datalen);
 	pcrsize = htonl(pcrinfosize);
@@ -601,9 +608,12 @@ static int tpm_unseal(struct tpm_buf *tb,
 
 	ordinal = htonl(TPM_ORD_UNSEAL);
 	ret = tpm_get_random(chip, nonceodd, TPM_NONCE_SIZE);
+	if (ret < 0)
+		return ret;
+
 	if (ret != TPM_NONCE_SIZE) {
 		pr_info("trusted_key: tpm_get_random failed (%d)\n", ret);
-		return ret;
+		return -EIO;
 	}
 	ret = TSS_authhmac(authdata1, keyauth, TPM_NONCE_SIZE,
 			   enonce1, nonceodd, cont, sizeof(uint32_t),
@@ -1013,8 +1023,12 @@ static int trusted_instantiate(struct key *key,
 	case Opt_new:
 		key_len = payload->key_len;
 		ret = tpm_get_random(chip, payload->key, key_len);
+		if (ret < 0)
+			goto out;
+
 		if (ret != key_len) {
 			pr_info("trusted_key: key_create failed (%d)\n", ret);
+			ret = -EIO;
 			goto out;
 		}
 		if (tpm2)
-- 
2.25.1