From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Tadeusz Struk <tadeusz.struk@intel.com>,
grawity@gmail.com, linux-integrity@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tpm: fix a race between poll and write in tpm-dev-common
Date: Thu, 21 Mar 2019 15:34:23 +0200 [thread overview]
Message-ID: <20190321133423.GC2267@linux.intel.com> (raw)
In-Reply-To: <1552951167.2785.22.camel@HansenPartnership.com>
On Mon, Mar 18, 2019 at 04:19:27PM -0700, James Bottomley wrote:
> On Mon, 2019-03-18 at 15:18 -0700, Tadeusz Struk wrote:
> > 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 <grawity@gmail.com>
> > Signed-off-by: Tadeusz Struk <tadeusz.struk@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);
>
> This doesn't do anything to address the theory that the queued work
> hasn't run before the poll wakes up, does it? If you have an
> alternative theory, could you explain it?
I see now what you mean.
Tadeusz: before you send a new patch put this comment to that place
as a reminder:
/* Checking only response_length is correct because write() always zeros
* it and poll() should succeed after the first partial read.
*/
/Jarkko
next prev parent reply other threads:[~2019-03-21 13:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-18 22:18 [PATCH] tpm: fix a race between poll and write in tpm-dev-common Tadeusz Struk
2019-03-18 23:19 ` James Bottomley
2019-03-19 19:09 ` Tadeusz Struk
2019-03-21 13:34 ` Jarkko Sakkinen [this message]
2019-03-21 13:34 ` Jarkko Sakkinen
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