tpm: fix an invalid condition in tpm_common_poll

tstruk · James Morris · commit 711062926346 · 2019-04-08T15:58:53.000-07:00
The poll condition should only check response_length, because reads should only be issued if there is data to read. The response_read flag only prevents double writes. The problem was that the write set the response_read to false, enqued a tpm job, and returned. Then application called poll which checked the response_read flag and returned EPOLLIN. Then the application called read, but got nothing. After all that the async_work kicked in. Added also mutex_lock around the poll check to prevent other possible race conditions. Fixes: 9488585 ("tpm: add support for partial reads") Reported-by: Mantas Mikulėnas <grawity@gmail.com> Tested-by: Mantas Mikulėnas <grawity@gmail.com> 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: James Morris <james.morris@microsoft.com>
diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
@@ -233,12 +233,19 @@ __poll_t tpm_common_poll(struct file *file, poll_table *wait)
 	__poll_t mask = 0;
 
 	poll_wait(file, &priv->async_wait, wait);
+	mutex_lock(&priv->buffer_mutex);
 
-	if (!priv->response_read || priv->response_length)
+	/*
+	 * The response_length indicates if there is still response
+	 * (or part of it) to be consumed. Partial reads decrease it
+	 * by the number of bytes read, and write resets it the zero.
+	 */
+	if (priv->response_length)
 		mask = EPOLLIN | EPOLLRDNORM;
 	else
 		mask = EPOLLOUT | EPOLLWRNORM;
 
+	mutex_unlock(&priv->buffer_mutex);
 	return mask;
 }
 
