From: Jason Gunthorpe <jgg@ziepe.ca>
To: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: Lino Sanfilippo <l.sanfilippo@kunbus.com>,
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 20:39:06 -0400 [thread overview]
Message-ID: <20210206003906.GR4718@ziepe.ca> (raw)
In-Reply-To: <db7c90c3-d86a-65c9-81a2-be1527b47e11@gmx.de>
On Fri, Feb 05, 2021 at 10:50:02PM +0100, Lino Sanfilippo wrote:
> On 05.02.21 at 16:58, Jason Gunthorpe wrote:
> eference in the first place).
> >
> > No, they are all chained together because they are all in the same
> > struct:
> >
> > struct tpm_chip {
> > struct device dev;
> > struct device devs;
> > struct cdev cdev;
> > struct cdev cdevs;
> >
> > dev holds the refcount on memory, when it goes 0 the whole thing is
> > kfreed.
> >
> > The rule is dev's refcount can't go to zero while any other refcount
> > is != 0.
> >
> > For instance devs holds a get on dev that is put back only when devs
> > goes to 0:
> >
> > static void tpm_devs_release(struct device *dev)
> > {
> > struct tpm_chip *chip = container_of(dev, struct tpm_chip, devs);
> >
> > /* release the master device reference */
> > put_device(&chip->dev);
> > }
> >
> > Both cdev elements do something similar inside the cdev layer.
>
> Well this chaining is exactly what does not work nowadays and what the patch is supposed
> to fix: currently we dont ever take the extra ref (not even in TPM 2 case, note that
> TPM_CHIP_FLAG_TMP2 is never set), so
>
> - if (chip->flags & TPM_CHIP_FLAG_TPM2)
> - get_device(&chip->dev);
> + get_device(&chip->dev);
Oh, hah, yes that is busted up. The patch sketch I sent to James is
the right way to handle it, feel free to take it up
> and tpm_devs_release() is never called, since there is nothing that ever puts devs, so
Yes, that is a pre-existing memory leak
> The race with only get_device()/putdevice() in tpm_common_open()/tpm_common_release() is:
The refcount handling is busted up and not working the way it is
designed, when that is fixed there is no race.
Jason
next prev parent reply other threads:[~2021-02-06 3:20 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
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 [this message]
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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