tpm: fix an invalid condition in tpm_common_poll

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: 9488585b21bef0df12 ("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
index 8856cce..817ae09 100644 (file)
--- 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;
 }