[PATCH 1/1][SRU][D] tpm: fix an invalid condition in tpm_common_poll

Ivan Hu ivan.hu at canonical.com
Mon Jun 24 08:10:13 UTC 2019

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

BugLink: https://bugs.launchpad.net/bugs/1833297

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 Mikul─Śnas <grawity at gmail.com>
Tested-by: Mantas Mikul─Śnas <grawity at gmail.com>
Signed-off-by: Tadeusz Struk <tadeusz.struk at intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen at linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen at linux.intel.com>
Signed-off-by: James Morris <james.morris at microsoft.com>
(cherry picked from commit 7110629263469b4664d00b38ef80a656eddf3637)
Signed-off-by: Ivan Hu <ivan.hu at canonical.com>
 drivers/char/tpm/tpm-dev-common.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
index 5eecad233ea1..744b0237300a 100644
--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -203,12 +203,19 @@ __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)
+	mutex_unlock(&priv->buffer_mutex);
 	return mask;

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