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tpm: fix race condition in tpm_common_write()

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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: 1da177e4c3 ("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>
This commit is contained in:
Tadeusz Struk 2018-05-22 14:37:18 -07:00 committed by Jarkko Sakkinen
parent 424eaf910c
commit 3ab2011ea3
2 changed files with 20 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
drivers/char/tpm/tpm-dev-common.c
View File

@ -37,7 +37,7 @@ static void timeout_work(struct work_struct *work)
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 tpm_chip *chip,
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 *file, char __user *buf,
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);
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;
}
@ -91,18 +85,20 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
size_t in_size = size;
ssize_t out_size;
/* 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)
return -EBUSY;
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 (priv->data_pending != 0) {
mutex_unlock(&priv->buffer_mutex);
return -EBUSY;
}
if (copy_from_user
(priv->data_buffer, (void __user *) buf, in_size)) {
mutex_unlock(&priv->buffer_mutex);
@ -132,7 +128,7 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
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 *file, struct file_priv *priv)
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;
}

2
drivers/char/tpm/tpm-dev.h
View File

@ -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 */