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Subject[PATCH 4.17 082/220] tpm: fix race condition in tpm_common_write()
Date
4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tadeusz Struk <tadeusz.struk@intel.com>

commit 3ab2011ea368ec3433ad49e1b9e1c7b70d2e65df upstream.

There is a race condition in tpm_common_write function allowing
two threads on the same /dev/tpm<N>, or two different applications
on the same /dev/tpmrm<N> to overwrite each other commands/responses.
Fixed this by taking the priv->buffer_mutex early in the function.

Also converted the priv->data_pending from atomic to a regular size_t
type. There is no need for it to be atomic since it is only touched
under the protection of the priv->buffer_mutex.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/char/tpm/tpm-dev-common.c | 40 +++++++++++++++++---------------------
drivers/char/tpm/tpm-dev.h | 2 -
2 files changed, 19 insertions(+), 23 deletions(-)

--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -37,7 +37,7 @@ static void timeout_work(struct work_str
struct file_priv *priv = container_of(work, struct file_priv, work);

mutex_lock(&priv->buffer_mutex);
- atomic_set(&priv->data_pending, 0);
+ priv->data_pending = 0;
memset(priv->data_buffer, 0, sizeof(priv->data_buffer));
mutex_unlock(&priv->buffer_mutex);
}
@@ -46,7 +46,6 @@ void tpm_common_open(struct file *file,
struct file_priv *priv)
{
priv->chip = chip;
- atomic_set(&priv->data_pending, 0);
mutex_init(&priv->buffer_mutex);
timer_setup(&priv->user_read_timer, user_reader_timeout, 0);
INIT_WORK(&priv->work, timeout_work);
@@ -58,29 +57,24 @@ ssize_t tpm_common_read(struct file *fil
size_t size, loff_t *off)
{
struct file_priv *priv = file->private_data;
- ssize_t ret_size;
- ssize_t orig_ret_size;
+ ssize_t ret_size = 0;
int rc;

del_singleshot_timer_sync(&priv->user_read_timer);
flush_work(&priv->work);
- ret_size = atomic_read(&priv->data_pending);
- if (ret_size > 0) { /* relay data */
- orig_ret_size = ret_size;
- if (size < ret_size)
- ret_size = size;
+ mutex_lock(&priv->buffer_mutex);

- mutex_lock(&priv->buffer_mutex);
+ if (priv->data_pending) {
+ ret_size = min_t(ssize_t, size, priv->data_pending);
rc = copy_to_user(buf, priv->data_buffer, ret_size);
- memset(priv->data_buffer, 0, orig_ret_size);
+ memset(priv->data_buffer, 0, priv->data_pending);
if (rc)
ret_size = -EFAULT;

- mutex_unlock(&priv->buffer_mutex);
+ priv->data_pending = 0;
}

- atomic_set(&priv->data_pending, 0);
-
+ mutex_unlock(&priv->buffer_mutex);
return ret_size;
}

@@ -91,17 +85,19 @@ ssize_t tpm_common_write(struct file *fi
size_t in_size = size;
ssize_t out_size;

+ if (in_size > TPM_BUFSIZE)
+ return -E2BIG;
+
+ mutex_lock(&priv->buffer_mutex);
+
/* Cannot perform a write until the read has cleared either via
* tpm_read or a user_read_timer timeout. This also prevents split
* buffered writes from blocking here.
*/
- if (atomic_read(&priv->data_pending) != 0)
+ if (priv->data_pending != 0) {
+ mutex_unlock(&priv->buffer_mutex);
return -EBUSY;
-
- if (in_size > TPM_BUFSIZE)
- return -E2BIG;
-
- mutex_lock(&priv->buffer_mutex);
+ }

if (copy_from_user
(priv->data_buffer, (void __user *) buf, in_size)) {
@@ -132,7 +128,7 @@ ssize_t tpm_common_write(struct file *fi
return out_size;
}

- atomic_set(&priv->data_pending, out_size);
+ priv->data_pending = out_size;
mutex_unlock(&priv->buffer_mutex);

/* Set a timeout by which the reader must come claim the result */
@@ -149,5 +145,5 @@ void tpm_common_release(struct file *fil
del_singleshot_timer_sync(&priv->user_read_timer);
flush_work(&priv->work);
file->private_data = NULL;
- atomic_set(&priv->data_pending, 0);
+ priv->data_pending = 0;
}
--- a/drivers/char/tpm/tpm-dev.h
+++ b/drivers/char/tpm/tpm-dev.h
@@ -8,7 +8,7 @@ struct file_priv {
struct tpm_chip *chip;

/* Data passed to and from the tpm via the read/write calls */
- atomic_t data_pending;
+ size_t data_pending;
struct mutex buffer_mutex;

struct timer_list user_read_timer; /* user needs to claim result */

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