[PATCH] tpm: fix a race between poll and write in tpm-dev-common

[Tadeusz Struk]

Since the poll returns EPOLLIN base on the state of two
variables, the response_read being false and the
response_length > 0 the poll needs to take the buffer_mutex
after it is woken up.

Fixes: 9488585b21bef0df12 ("tpm: add support for partial reads")
Reported-by: Mantas Mikulėnas <graw...@gmail.com>
Signed-off-by: Tadeusz Struk <tadeusz.st...@intel.com>
---
 drivers/char/tpm/tpm-dev-common.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/char/tpm/tpm-dev-common.c 
b/drivers/char/tpm/tpm-dev-common.c
index 5eecad233ea1..61e458d6f652 100644
--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -203,12 +203,14 @@ __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)
                mask = EPOLLIN | EPOLLRDNORM;
        else
                mask = EPOLLOUT | EPOLLWRNORM;
 
+       mutex_unlock(&priv->buffer_mutex);
        return mask;
 }