linux-kernel - Re: [PATCH v2] tpm: fix an invalid condition in tpm_common

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Message-ID: <CAPWNY8UmDAKeF+SNMKDxki=-=s+UPx9WXQvSoFqWmUCsNvv=1g@mail.gmail.com>
Date:   Wed, 20 Mar 2019 20:51:30 +0200
From:   Mantas Mikulėnas <grawity@...il.com>
To:     Tadeusz Struk <tadeusz.struk@...el.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James.Bottomley@...senpartnership.com,
        linux-integrity@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tpm: fix an invalid condition in tpm_common_poll

On Tue, Mar 19, 2019 at 10:31 PM Tadeusz Struk <tadeusz.struk@...el.com> 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@...il.com>
> Signed-off-by: Tadeusz Struk <tadeusz.struk@...el.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);
>         return mask;
>  }

Thanks, this patch seems to work, and I apologize for not responding
to test the patches earlier.

Any chance it'll be submitted for stable 5.0.x as well?

-- 
Mantas Mikulėnas