From: Jason Gunthorpe <jgg@ziepe.ca>
To: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>,
peterhuewe@gmx.de, jarkko@kernel.org, stefanb@linux.vnet.ibm.com,
James.Bottomley@hansenpartnership.com, stable@vger.kernel.org,
linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip
Date: Fri, 5 Feb 2021 11:15:11 -0400 [thread overview]
Message-ID: <20210205151511.GM4718@ziepe.ca> (raw)
In-Reply-To: <3b821bf9-0f54-3473-d934-61c0c29f8957@kunbus.com>
On Fri, Feb 05, 2021 at 03:55:09PM +0100, Lino Sanfilippo wrote:
> Hi,
>
> On 05.02.21 14:05, Jason Gunthorpe wrote:
>
> >>
> >> Commit fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm<n>")
> >> already introduced function tpm_devs_release() to release the extra
> >> reference but did not implement the required put on chip->devs that results
> >> in the call of this function.
> >
> > Seems wonky, the devs is just supposed to be a side thing, nothing
> > should be using it as a primary reference count for a tpm.
> >
> > The bug here is only that tpm_common_open() did not get a kref on the
> > chip before putting it in priv and linking it to the fd. See the
> > comment before tpm_try_get_ops() indicating the caller must already
> > have taken care to ensure the chip is valid.
> >
> > This should be all you need to fix the oops:
> >
> > diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
> > index 1784530b8387bb..1b738dca7fffb5 100644
> > +++ b/drivers/char/tpm/tpm-dev-common.c
> > @@ -105,6 +105,7 @@ static void tpm_timeout_work(struct work_struct *work)
> > void tpm_common_open(struct file *file, struct tpm_chip *chip,
> > struct file_priv *priv, struct tpm_space *space)
> > {
> > + get_device(&priv->chip.dev);
> > priv->chip = chip;
> > priv->space = space;
> > priv->response_read = true;
>
> This is racy, isnt it? The time between we open the file and we want to grab the
> reference in common_open() the chip can already be unregistered and freed.
No, the cdev layer holds the refcount on the device while open is
being called.
Jason
next prev parent reply other threads:[~2021-02-05 22:24 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-04 23:50 [PATCH v3 0/2] TPM fixes Lino Sanfilippo
2021-02-04 23:50 ` [PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip Lino Sanfilippo
2021-02-05 0:46 ` Stefan Berger
2021-02-05 1:44 ` Stefan Berger
2021-02-05 2:01 ` James Bottomley
2021-02-05 10:52 ` Lino Sanfilippo
2021-02-05 13:29 ` Stefan Berger
2021-02-05 10:34 ` Lino Sanfilippo
2021-02-05 6:50 ` Greg KH
2021-02-05 13:05 ` Jason Gunthorpe
2021-02-05 14:55 ` Lino Sanfilippo
2021-02-05 15:15 ` Jason Gunthorpe [this message]
2021-02-05 15:50 ` Lino Sanfilippo
2021-02-05 15:58 ` Jason Gunthorpe
2021-02-05 21:50 ` Lino Sanfilippo
2021-02-06 0:39 ` Jason Gunthorpe
2021-02-04 23:50 ` [PATCH v3 2/2] tpm: in tpm2_del_space check if ops pointer is still valid Lino Sanfilippo
2021-02-05 0:34 ` James Bottomley
2021-02-05 2:18 ` Jarkko Sakkinen
2021-02-05 16:48 ` James Bottomley
2021-02-05 17:25 ` Jason Gunthorpe
2021-02-05 17:54 ` James Bottomley
2021-02-06 1:02 ` Jason Gunthorpe
2021-02-06 1:08 ` James Bottomley
2021-02-06 1:34 ` Jason Gunthorpe
2021-02-09 11:52 ` Lino Sanfilippo
2021-02-09 13:36 ` Jason Gunthorpe
2021-02-09 13:39 ` Lino Sanfilippo
2021-02-12 11:02 ` Jarkko Sakkinen
2021-02-12 10:59 ` Jarkko Sakkinen
2021-02-14 17:22 ` Lino Sanfilippo
2021-02-05 10:30 ` Lino Sanfilippo
2021-03-06 16:07 ` Lino Sanfilippo
2021-02-05 6:51 ` Greg KH
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