[PATCH] tpm: fix a race condition tpm2_unseal_trusted()

[Jarkko Sakkinen]

Unseal and load operations should be done as an atomic operation. This
commit introduces unlocked tpm_transmit() so that tpm2_unseal_trusted()
can do the locking by itself.

v2: Introduced an unlocked unseal operation instead of changing locking
    strategy in order to make less intrusive bug fix and thus more
    backportable.

v3: Have also separate __tpm_transmit() that takes 'flags' in order to
    better localize the bug fix and make it easier to backport.

v4: Cleaned up the control flow in tpm2_unseal_trusted. Added the
    missing 'Fixes' line.

Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0 chips")
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
---
 drivers/char/tpm/tpm-interface.c | 16 +++++++++-------
 drivers/char/tpm/tpm.h           | 25 +++++++++++++++++++++----
 drivers/char/tpm/tpm2-cmd.c      | 12 ++++++++----
 3 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 43ef0ef..80e702a 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -330,8 +330,8 @@ EXPORT_SYMBOL_GPL(tpm_calc_ordinal_duration);
 /*
  * Internal kernel interface to transmit TPM commands
  */
-ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
-		     size_t bufsiz)
+ssize_t __tpm_transmit(struct tpm_chip *chip, const char *buf,
+		       size_t bufsiz, unsigned int flags)
 {
 	ssize_t rc;
 	u32 count, ordinal;
@@ -350,7 +350,8 @@ ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
 		return -E2BIG;
 	}
 
-	mutex_lock(&chip->tpm_mutex);
+	if (flags & TPM_TRANSMIT_LOCK)
+		mutex_lock(&chip->tpm_mutex);
 
 	rc = chip->ops->send(chip, (u8 *) buf, count);
 	if (rc < 0) {
@@ -393,20 +394,21 @@ out_recv:
 		dev_err(&chip->dev,
 			"tpm_transmit: tpm_recv: error %zd\n", rc);
 out:
-	mutex_unlock(&chip->tpm_mutex);
+	if (flags & TPM_TRANSMIT_LOCK)
+		mutex_unlock(&chip->tpm_mutex);
 	return rc;
 }
 
 #define TPM_DIGEST_SIZE 20
 #define TPM_RET_CODE_IDX 6
 
-ssize_t tpm_transmit_cmd(struct tpm_chip *chip, void *cmd,
-			 int len, const char *desc)
+ssize_t __tpm_transmit_cmd(struct tpm_chip *chip, void *cmd,
+			   int len, const char *desc, unsigned int flags)
 {
 	struct tpm_output_header *header;
 	int err;
 
-	len = tpm_transmit(chip, (u8 *) cmd, len);
+	len = __tpm_transmit(chip, cmd, len, flags);
 	if (len <  0)
 		return len;
 	else if (len < TPM_HEADER_SIZE)
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 6e002c4..0a4abf0 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -476,12 +476,29 @@ extern dev_t tpm_devt;
 extern const struct file_operations tpm_fops;
 extern struct idr dev_nums_idr;
 
+enum tpm_transmit_flags {
+	TPM_TRANSMIT_LOCK,
+};
+
+ssize_t __tpm_transmit(struct tpm_chip *chip, const char *buf,
+		       size_t bufsiz, unsigned int flags);
+ssize_t __tpm_transmit_cmd(struct tpm_chip *chip, void *cmd, int len,
+			   const char *desc, unsigned int flags);
+
+static inline ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
+				   size_t bufsiz)
+{
+	return __tpm_transmit(chip, buf, bufsiz, TPM_TRANSMIT_LOCK);
+}
+
+static inline ssize_t tpm_transmit_cmd(struct tpm_chip *chip, void *cmd,
+				       int len, const char *desc)
+{
+	return __tpm_transmit_cmd(chip, cmd, len, desc, TPM_TRANSMIT_LOCK);
+}
+
 ssize_t tpm_getcap(struct tpm_chip *chip, __be32 subcap_id, cap_t *cap,
 		   const char *desc);
-ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
-		     size_t bufsiz);
-ssize_t tpm_transmit_cmd(struct tpm_chip *chip, void *cmd, int len,
-			 const char *desc);
 int tpm_get_timeouts(struct tpm_chip *chip);
 int tpm1_auto_startup(struct tpm_chip *chip);
 int tpm_do_selftest(struct tpm_chip *chip);
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 499f405..a2a0314 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -576,7 +576,7 @@ static int tpm2_load(struct tpm_chip *chip,
 		goto out;
 	}
 
-	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "loading blob");
+	rc = __tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "loading blob", 0);
 	if (!rc)
 		*blob_handle = be32_to_cpup(
 			(__be32 *) &buf.data[TPM_HEADER_SIZE]);
@@ -604,7 +604,8 @@ static void tpm2_flush_context(struct tpm_chip *chip, u32 handle)
 
 	tpm_buf_append_u32(&buf, handle);
 
-	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "flushing context");
+	rc = __tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "flushing context",
+				0);
 	if (rc)
 		dev_warn(&chip->dev, "0x%08x was not flushed, rc=%d\n", handle,
 			 rc);
@@ -635,7 +636,7 @@ static int tpm2_unseal(struct tpm_chip *chip,
 			     options->blobauth /* hmac */,
 			     TPM_DIGEST_SIZE);
 
-	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "unsealing");
+	rc = __tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "unsealing", 0);
 	if (rc > 0)
 		rc = -EPERM;
 
@@ -668,14 +669,17 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
 	u32 blob_handle;
 	int rc;
 
+	mutex_lock(&chip->tpm_mutex);
 	rc = tpm2_load(chip, payload, options, &blob_handle);
 	if (rc)
-		return rc;
+		goto out;
 
 	rc = tpm2_unseal(chip, payload, options, blob_handle);
 
 	tpm2_flush_context(chip, blob_handle);
 
+out:
+	mutex_unlock(&chip->tpm_mutex);
 	return rc;
 }
 
-- 
2.7.4