tpm: fix a race condition in tpm2_unseal_trusted()

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.

Fixes: 0fe54803 ("keys, trusted: seal/unseal with TPM 2.0 chips")
Cc: stable@vger.kernel.org
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>

drivers/char/tpm/tpm-dev.c

@@ -145,7 +145,7 @@ static ssize_t tpm_write(struct file *file, const char __user *buf,
 		return -EPIPE;
 	}
 	out_size = tpm_transmit(priv->chip, priv->data_buffer,
-				sizeof(priv->data_buffer));
+				sizeof(priv->data_buffer), 0);
 
 	tpm_put_ops(priv->chip);
 	if (out_size < 0) {

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 u8 *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_UNLOCKED))
+		mutex_lock(&chip->tpm_mutex);
 
 	rc = chip->ops->send(chip, (u8 *) buf, count);
 	if (rc < 0) {
@@ -393,20 +394,21 @@ ssize_t tpm_transmit(struct tpm_chip *chip, const char *buf,
 		dev_err(&chip->dev,
 			"tpm_transmit: tpm_recv: error %zd\n", rc);
 out:
-	mutex_unlock(&chip->tpm_mutex);
+	if (!(flags & TPM_TRANSMIT_UNLOCKED))
+		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, const void *cmd,
+			 int len, unsigned int flags, const char *desc)
 {
-	struct tpm_output_header *header;
+	const struct tpm_output_header *header;
 	int err;
 
-	len = tpm_transmit(chip, (u8 *) cmd, len);
+	len = tpm_transmit(chip, (const u8 *)cmd, len, flags);
 	if (len <  0)
 		return len;
 	else if (len < TPM_HEADER_SIZE)
@@ -453,7 +455,8 @@ ssize_t tpm_getcap(struct tpm_chip *chip, __be32 subcap_id, cap_t *cap,
 		tpm_cmd.params.getcap_in.subcap_size = cpu_to_be32(4);
 		tpm_cmd.params.getcap_in.subcap = subcap_id;
 	}
-	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE, desc);
+	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE, 0,
+			      desc);
 	if (!rc)
 		*cap = tpm_cmd.params.getcap_out.cap;
 	return rc;
@@ -469,7 +472,7 @@ void tpm_gen_interrupt(struct tpm_chip *chip)
 	tpm_cmd.params.getcap_in.subcap_size = cpu_to_be32(4);
 	tpm_cmd.params.getcap_in.subcap = TPM_CAP_PROP_TIS_TIMEOUT;
 
-	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE,
+	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE, 0,
 			      "attempting to determine the timeouts");
 }
 EXPORT_SYMBOL_GPL(tpm_gen_interrupt);
@@ -490,7 +493,7 @@ static int tpm_startup(struct tpm_chip *chip, __be16 startup_type)
 	start_cmd.header.in = tpm_startup_header;
 
 	start_cmd.params.startup_in.startup_type = startup_type;
-	return tpm_transmit_cmd(chip, &start_cmd, TPM_INTERNAL_RESULT_SIZE,
+	return tpm_transmit_cmd(chip, &start_cmd, TPM_INTERNAL_RESULT_SIZE, 0,
 				"attempting to start the TPM");
 }
 
@@ -521,7 +524,8 @@ int tpm_get_timeouts(struct tpm_chip *chip)
 	tpm_cmd.params.getcap_in.cap = TPM_CAP_PROP;
 	tpm_cmd.params.getcap_in.subcap_size = cpu_to_be32(4);
 	tpm_cmd.params.getcap_in.subcap = TPM_CAP_PROP_TIS_TIMEOUT;
-	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE, NULL);
+	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE, 0,
+			      NULL);
 
 	if (rc == TPM_ERR_INVALID_POSTINIT) {
 		/* The TPM is not started, we are the first to talk to it.
@@ -535,7 +539,7 @@ int tpm_get_timeouts(struct tpm_chip *chip)
 		tpm_cmd.params.getcap_in.subcap_size = cpu_to_be32(4);
 		tpm_cmd.params.getcap_in.subcap = TPM_CAP_PROP_TIS_TIMEOUT;
 		rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE,
-				  NULL);
+				      0, NULL);
 	}
 	if (rc) {
 		dev_err(&chip->dev,
@@ -596,7 +600,7 @@ int tpm_get_timeouts(struct tpm_chip *chip)
 	tpm_cmd.params.getcap_in.subcap_size = cpu_to_be32(4);
 	tpm_cmd.params.getcap_in.subcap = TPM_CAP_PROP_TIS_DURATION;
 
-	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE,
+	rc = tpm_transmit_cmd(chip, &tpm_cmd, TPM_INTERNAL_RESULT_SIZE, 0,
 			      "attempting to determine the durations");
 	if (rc)
 		return rc;
@@ -652,7 +656,7 @@ static int tpm_continue_selftest(struct tpm_chip *chip)
 	struct tpm_cmd_t cmd;
 
 	cmd.header.in = continue_selftest_header;
-	rc = tpm_transmit_cmd(chip, &cmd, CONTINUE_SELFTEST_RESULT_SIZE,
+	rc = tpm_transmit_cmd(chip, &cmd, CONTINUE_SELFTEST_RESULT_SIZE, 0,
 			      "continue selftest");
 	return rc;
 }
@@ -672,7 +676,7 @@ int tpm_pcr_read_dev(struct tpm_chip *chip, int pcr_idx, u8 *res_buf)
 
 	cmd.header.in = pcrread_header;
 	cmd.params.pcrread_in.pcr_idx = cpu_to_be32(pcr_idx);
-	rc = tpm_transmit_cmd(chip, &cmd, READ_PCR_RESULT_SIZE,
+	rc = tpm_transmit_cmd(chip, &cmd, READ_PCR_RESULT_SIZE, 0,
 			      "attempting to read a pcr value");
 
 	if (rc == 0)
@@ -770,7 +774,7 @@ int tpm_pcr_extend(u32 chip_num, int pcr_idx, const u8 *hash)
 	cmd.header.in = pcrextend_header;
 	cmd.params.pcrextend_in.pcr_idx = cpu_to_be32(pcr_idx);
 	memcpy(cmd.params.pcrextend_in.hash, hash, TPM_DIGEST_SIZE);
-	rc = tpm_transmit_cmd(chip, &cmd, EXTEND_PCR_RESULT_SIZE,
+	rc = tpm_transmit_cmd(chip, &cmd, EXTEND_PCR_RESULT_SIZE, 0,
 			      "attempting extend a PCR value");
 
 	tpm_put_ops(chip);
@@ -809,7 +813,7 @@ int tpm_do_selftest(struct tpm_chip *chip)
 		/* Attempt to read a PCR value */
 		cmd.header.in = pcrread_header;
 		cmd.params.pcrread_in.pcr_idx = cpu_to_be32(0);
-		rc = tpm_transmit(chip, (u8 *) &cmd, READ_PCR_RESULT_SIZE);
+		rc = tpm_transmit(chip, (u8 *) &cmd, READ_PCR_RESULT_SIZE, 0);
 		/* Some buggy TPMs will not respond to tpm_tis_ready() for
 		 * around 300ms while the self test is ongoing, keep trying
 		 * until the self test duration expires. */
@@ -879,7 +883,7 @@ int tpm_send(u32 chip_num, void *cmd, size_t buflen)
 	if (chip == NULL)
 		return -ENODEV;
 
-	rc = tpm_transmit_cmd(chip, cmd, buflen, "attempting tpm_cmd");
+	rc = tpm_transmit_cmd(chip, cmd, buflen, 0, "attempting tpm_cmd");
 
 	tpm_put_ops(chip);
 	return rc;
@@ -981,14 +985,15 @@ int tpm_pm_suspend(struct device *dev)
 		cmd.params.pcrextend_in.pcr_idx = cpu_to_be32(tpm_suspend_pcr);
 		memcpy(cmd.params.pcrextend_in.hash, dummy_hash,
 		       TPM_DIGEST_SIZE);
-		rc = tpm_transmit_cmd(chip, &cmd, EXTEND_PCR_RESULT_SIZE,
+		rc = tpm_transmit_cmd(chip, &cmd, EXTEND_PCR_RESULT_SIZE, 0,
 				      "extending dummy pcr before suspend");
 	}
 
 	/* now do the actual savestate */
 	for (try = 0; try < TPM_RETRY; try++) {
 		cmd.header.in = savestate_header;
-		rc = tpm_transmit_cmd(chip, &cmd, SAVESTATE_RESULT_SIZE, NULL);
+		rc = tpm_transmit_cmd(chip, &cmd, SAVESTATE_RESULT_SIZE, 0,
+				      NULL);
 
 		/*
 		 * If the TPM indicates that it is too busy to respond to
@@ -1072,8 +1077,8 @@ int tpm_get_random(u32 chip_num, u8 *out, size_t max)
 		tpm_cmd.params.getrandom_in.num_bytes = cpu_to_be32(num_bytes);
 
 		err = tpm_transmit_cmd(chip, &tpm_cmd,
-				   TPM_GETRANDOM_RESULT_SIZE + num_bytes,
-				   "attempting get random");
+				       TPM_GETRANDOM_RESULT_SIZE + num_bytes,
+				       0, "attempting get random");
 		if (err)
 			break;
 

drivers/char/tpm/tpm-sysfs.c

@@ -39,7 +39,7 @@ static ssize_t pubek_show(struct device *dev, struct device_attribute *attr,
 	struct tpm_chip *chip = to_tpm_chip(dev);
 
 	tpm_cmd.header.in = tpm_readpubek_header;
-	err = tpm_transmit_cmd(chip, &tpm_cmd, READ_PUBEK_RESULT_SIZE,
+	err = tpm_transmit_cmd(chip, &tpm_cmd, READ_PUBEK_RESULT_SIZE, 0,
 			       "attempting to read the PUBEK");
 	if (err)
 		goto out;

drivers/char/tpm/tpm.h

@@ -476,12 +476,16 @@ extern dev_t tpm_devt;
 extern const struct file_operations tpm_fops;
 extern struct idr dev_nums_idr;
 
+enum tpm_transmit_flags {
+	TPM_TRANSMIT_UNLOCKED	= BIT(0),
+};
+
+ssize_t tpm_transmit(struct tpm_chip *chip, const u8 *buf, size_t bufsiz,
+		     unsigned int flags);
+ssize_t tpm_transmit_cmd(struct tpm_chip *chip, const void *cmd, int len,
+			 unsigned int flags, const char *desc);
 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);
 extern int tpm_get_timeouts(struct tpm_chip *);
 extern void tpm_gen_interrupt(struct tpm_chip *);
 int tpm1_auto_startup(struct tpm_chip *chip);

drivers/char/tpm/tpm2-cmd.c

@@ -282,7 +282,7 @@ int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u8 *res_buf)
 	       sizeof(cmd.params.pcrread_in.pcr_select));
 	cmd.params.pcrread_in.pcr_select[pcr_idx >> 3] = 1 << (pcr_idx & 0x7);
 
-	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd),
+	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0,
 			      "attempting to read a pcr value");
 	if (rc == 0) {
 		buf = cmd.params.pcrread_out.digest;
@@ -330,7 +330,7 @@ int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, const u8 *hash)
 	cmd.params.pcrextend_in.hash_alg = cpu_to_be16(TPM2_ALG_SHA1);
 	memcpy(cmd.params.pcrextend_in.digest, hash, TPM_DIGEST_SIZE);
 
-	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd),
+	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0,
 			      "attempting extend a PCR value");
 
 	return rc;
@@ -376,7 +376,7 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *out, size_t max)
 		cmd.header.in = tpm2_getrandom_header;
 		cmd.params.getrandom_in.size = cpu_to_be16(num_bytes);
 
-		err = tpm_transmit_cmd(chip, &cmd, sizeof(cmd),
+		err = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0,
 				       "attempting get random");
 		if (err)
 			break;
@@ -434,12 +434,12 @@ static void tpm2_buf_append_auth(struct tpm_buf *buf, u32 session_handle,
 }
 
 /**
- * tpm2_seal_trusted() - seal a trusted key
- * @chip_num: A specific chip number for the request or TPM_ANY_NUM
- * @options: authentication values and other options
+ * tpm2_seal_trusted() - seal the payload of a trusted key
+ * @chip_num: TPM chip to use
  * @payload: the key data in clear and encrypted form
+ * @options: authentication values and other options
  *
- * Returns < 0 on error and 0 on success.
+ * Return: < 0 on error and 0 on success.
  */
 int tpm2_seal_trusted(struct tpm_chip *chip,
 		      struct trusted_key_payload *payload,
@@ -512,7 +512,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 		goto out;
 	}
 
-	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, "sealing data");
+	rc = tpm_transmit_cmd(chip, buf.data, PAGE_SIZE, 0, "sealing data");
 	if (rc)
 		goto out;
 
@@ -538,10 +538,18 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	return rc;
 }
 
-static int tpm2_load(struct tpm_chip *chip,
-		     struct trusted_key_payload *payload,
-		     struct trusted_key_options *options,
-		     u32 *blob_handle)
+/**
+ * tpm2_load_cmd() - execute a TPM2_Load command
+ * @chip_num: TPM chip to use
+ * @payload: the key data in clear and encrypted form
+ * @options: authentication values and other options
+ *
+ * Return: same as with tpm_transmit_cmd
+ */
+static int tpm2_load_cmd(struct tpm_chip *chip,
+			 struct trusted_key_payload *payload,
+			 struct trusted_key_options *options,
+			 u32 *blob_handle, unsigned int flags)
 {
 	struct tpm_buf buf;
 	unsigned int private_len;
@@ -576,7 +584,7 @@ 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, flags, "loading blob");
 	if (!rc)
 		*blob_handle = be32_to_cpup(
 			(__be32 *) &buf.data[TPM_HEADER_SIZE]);
@@ -590,7 +598,16 @@ static int tpm2_load(struct tpm_chip *chip,
 	return rc;
 }
 
-static void tpm2_flush_context(struct tpm_chip *chip, u32 handle)
+/**
+ * tpm2_flush_context_cmd() - execute a TPM2_FlushContext command
+ * @chip_num: TPM chip to use
+ * @payload: the key data in clear and encrypted form
+ * @options: authentication values and other options
+ *
+ * Return: same as with tpm_transmit_cmd
+ */
+static void tpm2_flush_context_cmd(struct tpm_chip *chip, u32 handle,
+				   unsigned int flags)
 {
 	struct tpm_buf buf;
 	int rc;
@@ -604,7 +621,8 @@ 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, flags,
+			      "flushing context");
 	if (rc)
 		dev_warn(&chip->dev, "0x%08x was not flushed, rc=%d\n", handle,
 			 rc);
@@ -612,10 +630,18 @@ static void tpm2_flush_context(struct tpm_chip *chip, u32 handle)
 	tpm_buf_destroy(&buf);
 }
 
-static int tpm2_unseal(struct tpm_chip *chip,
-		       struct trusted_key_payload *payload,
-		       struct trusted_key_options *options,
-		       u32 blob_handle)
+/**
+ * tpm2_unseal_cmd() - execute a TPM2_Unload command
+ * @chip_num: TPM chip to use
+ * @payload: the key data in clear and encrypted form
+ * @options: authentication values and other options
+ *
+ * Return: same as with tpm_transmit_cmd
+ */
+static int tpm2_unseal_cmd(struct tpm_chip *chip,
+			   struct trusted_key_payload *payload,
+			   struct trusted_key_options *options,
+			   u32 blob_handle, unsigned int flags)
 {
 	struct tpm_buf buf;
 	u16 data_len;
@@ -635,7 +661,7 @@ 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, flags, "unsealing");
 	if (rc > 0)
 		rc = -EPERM;
 
@@ -654,12 +680,12 @@ static int tpm2_unseal(struct tpm_chip *chip,
 }
 
 /**
- * tpm_unseal_trusted() - unseal a trusted key
- * @chip_num: A specific chip number for the request or TPM_ANY_NUM
- * @options: authentication values and other options
+ * tpm_unseal_trusted() - unseal the payload of a trusted key
+ * @chip_num: TPM chip to use
  * @payload: the key data in clear and encrypted form
+ * @options: authentication values and other options
  *
- * Returns < 0 on error and 0 on success.
+ * Return: < 0 on error and 0 on success.
  */
 int tpm2_unseal_trusted(struct tpm_chip *chip,
 			struct trusted_key_payload *payload,
@@ -668,14 +694,17 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
 	u32 blob_handle;
 	int rc;
 
-	rc = tpm2_load(chip, payload, options, &blob_handle);
+	mutex_lock(&chip->tpm_mutex);
+	rc = tpm2_load_cmd(chip, payload, options, &blob_handle,
+			   TPM_TRANSMIT_UNLOCKED);
 	if (rc)
-		return rc;
-
-	rc = tpm2_unseal(chip, payload, options, blob_handle);
-
-	tpm2_flush_context(chip, blob_handle);
+		goto out;
 
+	rc = tpm2_unseal_cmd(chip, payload, options, blob_handle,
+			     TPM_TRANSMIT_UNLOCKED);
+	tpm2_flush_context_cmd(chip, blob_handle, TPM_TRANSMIT_UNLOCKED);
+out:
+	mutex_unlock(&chip->tpm_mutex);
 	return rc;
 }
 
@@ -701,7 +730,7 @@ ssize_t tpm2_get_tpm_pt(struct tpm_chip *chip, u32 property_id,  u32 *value,
 	cmd.params.get_tpm_pt_in.property_id = cpu_to_be32(property_id);
 	cmd.params.get_tpm_pt_in.property_cnt = cpu_to_be32(1);
 
-	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), desc);
+	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0, desc);
 	if (!rc)
 		*value = be32_to_cpu(cmd.params.get_tpm_pt_out.value);
 
@@ -735,7 +764,7 @@ static int tpm2_startup(struct tpm_chip *chip, u16 startup_type)
 	cmd.header.in = tpm2_startup_header;
 
 	cmd.params.startup_in.startup_type = cpu_to_be16(startup_type);
-	return tpm_transmit_cmd(chip, &cmd, sizeof(cmd),
+	return tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0,
 				"attempting to start the TPM");
 }
 
@@ -763,7 +792,7 @@ void tpm2_shutdown(struct tpm_chip *chip, u16 shutdown_type)
 	cmd.header.in = tpm2_shutdown_header;
 	cmd.params.startup_in.startup_type = cpu_to_be16(shutdown_type);
 
-	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), "stopping the TPM");
+	rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0, "stopping the TPM");
 
 	/* In places where shutdown command is sent there's no much we can do
 	 * except print the error code on a system failure.
@@ -828,7 +857,7 @@ static int tpm2_start_selftest(struct tpm_chip *chip, bool full)
 	cmd.header.in = tpm2_selftest_header;
 	cmd.params.selftest_in.full_test = full;
 
-	rc = tpm_transmit_cmd(chip, &cmd, TPM2_SELF_TEST_IN_SIZE,
+	rc = tpm_transmit_cmd(chip, &cmd, TPM2_SELF_TEST_IN_SIZE, 0,
 			      "continue selftest");
 
 	/* At least some prototype chips seem to give RC_TESTING error
@@ -880,7 +909,7 @@ static int tpm2_do_selftest(struct tpm_chip *chip)
 		cmd.params.pcrread_in.pcr_select[1] = 0x00;
 		cmd.params.pcrread_in.pcr_select[2] = 0x00;
 
-		rc = tpm_transmit_cmd(chip, (u8 *) &cmd, sizeof(cmd), NULL);
+		rc = tpm_transmit_cmd(chip, &cmd, sizeof(cmd), 0, NULL);
 		if (rc < 0)
 			break;
 
@@ -928,7 +957,7 @@ int tpm2_probe(struct tpm_chip *chip)
 	cmd.params.get_tpm_pt_in.property_id = cpu_to_be32(0x100);
 	cmd.params.get_tpm_pt_in.property_cnt = cpu_to_be32(1);
 
-	rc = tpm_transmit(chip, (const char *) &cmd, sizeof(cmd));
+	rc = tpm_transmit(chip, (const u8 *)&cmd, sizeof(cmd), 0);
 	if (rc <  0)
 		return rc;
 	else if (rc < TPM_HEADER_SIZE)