From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Tadeusz Struk <tadeusz.struk@intel.com>, jarkko.sakkinen@linux.intel.com
Cc: grawity@gmail.com, linux-integrity@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll
Date: Wed, 20 Mar 2019 07:30:43 -0700 [thread overview]
Message-ID: <1553092243.2835.3.camel@HansenPartnership.com> (raw)
In-Reply-To: <155302749437.13955.651380639754310898.stgit@tstruk-mobl1.jf.intel.com>
On Tue, 2019-03-19 at 13:31 -0700, Tadeusz Struk wrote:
> 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>
> Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
> ---
> drivers/char/tpm/tpm-dev-common.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/tpm/tpm-dev-common.c
> b/drivers/char/tpm/tpm-dev-common.c
> index 5eecad233ea1..7312d3214381 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)
> + if (priv->response_length)
> mask = EPOLLIN | EPOLLRDNORM;
> else
> mask = EPOLLOUT | EPOLLWRNORM;
>
> + mutex_unlock(&priv->buffer_mutex);
Just an observation on this: the mutex is now no-longer necessary
because a read on a size_t quantity is always atomic.
James
next prev parent reply other threads:[~2019-03-20 14:30 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-19 20:31 [PATCH v2] tpm: fix an invalid condition in tpm_common_poll Tadeusz Struk
2019-03-20 14:30 ` James Bottomley [this message]
2019-03-20 14:49 ` Tadeusz Struk
2019-03-20 18:51 ` Mantas Mikulėnas
2019-03-20 19:18 ` Tadeusz Struk
2019-03-21 14:04 ` Jarkko Sakkinen
2019-03-21 13:59 ` Jarkko Sakkinen
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