linux-kernel - [PATCH v6 3/3] tpm: vtpm_proxy: Prevent userspace from sending driver command

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Date:   Wed, 24 May 2017 17:39:41 -0400
From:   Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:     jarkko.sakkinen@...ux.intel.com, tpmdd-devel@...ts.sourceforge.net
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, jgunthorpe@...idianresearch.com,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>
Subject: [PATCH v6 3/3] tpm: vtpm_proxy: Prevent userspace from sending driver command

To prevent userspace from sending the TPM driver command to set
the locality, we need to check every command that is sent from
user space. To distinguish user space commands from internally
sent commands we introduce an additional state flag
STATE_DRIVER_COMMAND that is set while the driver sends this
command. Similar to the TPM 2 space commands we return an error
code when this command is detected.

Signed-off-by: Stefan Berger <stefanb@...ux.vnet.ibm.com>
---
 drivers/char/tpm/tpm_vtpm_proxy.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
index 66024bf..1d877cc 100644
--- a/drivers/char/tpm/tpm_vtpm_proxy.c
+++ b/drivers/char/tpm/tpm_vtpm_proxy.c
@@ -43,6 +43,7 @@ struct proxy_dev {
 #define STATE_OPENED_FLAG        BIT(0)
 #define STATE_WAIT_RESPONSE_FLAG BIT(1)  /* waiting for emulator response */
 #define STATE_REGISTERED_FLAG	 BIT(2)
+#define STATE_DRIVER_COMMAND     BIT(3)  /* sending a driver specific command */
 
 	size_t req_len;              /* length of queued TPM request */
 	size_t resp_len;             /* length of queued TPM response */
@@ -299,6 +300,28 @@ static int vtpm_proxy_tpm_op_recv(struct tpm_chip *chip, u8 *buf, size_t count)
 	return len;
 }
 
+static int vtpm_proxy_is_driver_command(struct tpm_chip *chip,
+					u8 *buf, size_t count)
+{
+	struct tpm_input_header *hdr = (struct tpm_input_header *)buf;
+
+	if (count < sizeof(struct tpm_input_header))
+		return 0;
+
+	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+		switch (be32_to_cpu(hdr->ordinal)) {
+		case TPM2_CC_SET_LOCALITY:
+			return 1;
+		}
+	} else {
+		switch (be32_to_cpu(hdr->ordinal)) {
+		case TPM_ORD_SET_LOCALITY:
+			return 1;
+		}
+	}
+	return 0;
+}
+
 /*
  * Called when core TPM driver forwards TPM requests to 'server side'.
  *
@@ -321,6 +344,10 @@ static int vtpm_proxy_tpm_op_send(struct tpm_chip *chip, u8 *buf, size_t count)
 		return -EIO;
 	}
 
+	if (!(proxy_dev->state & STATE_DRIVER_COMMAND) &&
+	    vtpm_proxy_is_driver_command(chip, buf, count))
+		return -EFAULT;
+
 	mutex_lock(&proxy_dev->buf_lock);
 
 	if (!(proxy_dev->state & STATE_OPENED_FLAG)) {
@@ -376,6 +403,7 @@ static int vtpm_proxy_request_locality(struct tpm_chip *chip, int locality)
 	struct tpm_buf buf;
 	int rc;
 	const struct tpm_output_header *header;
+	struct proxy_dev *proxy_dev = dev_get_drvdata(&chip->dev);
 
 	if (chip->flags & TPM_CHIP_FLAG_TPM2)
 		rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS,
@@ -387,9 +415,14 @@ static int vtpm_proxy_request_locality(struct tpm_chip *chip, int locality)
 		return rc;
 	tpm_buf_append_u8(&buf, locality);
 
+	proxy_dev->state |= STATE_DRIVER_COMMAND;
+
 	rc = tpm_transmit_cmd(chip, NULL, buf.data, tpm_buf_length(&buf), 0,
 			      TPM_TRANSMIT_UNLOCKED | TPM_TRANSMIT_RAW,
 			      "attempting to set locality");
+
+	proxy_dev->state &= ~STATE_DRIVER_COMMAND;
+
 	if (rc < 0) {
 		locality = rc;
 		goto out;
-- 
2.4.3