From: Lino Sanfilippo <l.sanfilippo@kunbus.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: 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 15:55:09 +0100 [thread overview]
Message-ID: <3b821bf9-0f54-3473-d934-61c0c29f8957@kunbus.com> (raw)
In-Reply-To: <20210205130511.GI4718@ziepe.ca>
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
> --- a/drivers/char/tpm/tpm-dev-common.c
> +++ 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.
As a matter of fact this solution was the first thing that came into my mind, too,
until I noticed the possible race condition. I can only guess that this was what
James had in mind when he chose to take the extra reference to chip->dev in
tpm_chip_alloc() instead of common_open().
>> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>> index ddaeceb..3ace199 100644
>> +++ b/drivers/char/tpm/tpm-chip.c
>> @@ -360,8 +360,7 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>> * while cdevs is in use. The corresponding put
>> * is in the tpm_devs_release (TPM2 only)
>> */
>> - if (chip->flags & TPM_CHIP_FLAG_TPM2)
>> - get_device(&chip->dev);
>> + get_device(&chip->dev);
>>
>> if (chip->dev_num == 0)
>> chip->dev.devt = MKDEV(MISC_MAJOR, TPM_MINOR);
>> @@ -422,8 +421,21 @@ struct tpm_chip *tpmm_chip_alloc(struct device *pdev,
>> rc = devm_add_action_or_reset(pdev,
>> (void (*)(void *)) put_device,
>> &chip->dev);
>> - if (rc)
>> + if (rc) {
>> + put_device(&chip->devs);
>> return ERR_PTR(rc);
>
> This isn't right read what 'or_reset' does
>
In case of failure installing the action handler devm_add_action_or_reset() puts
chip->dev for us. But we also have put chip->devs since we have retrieved a
reference to both chip->dev and chip->devs. Or do I miss something here?
> Jason
>
Regards,
Lino
next prev parent reply other threads:[~2021-02-05 22:41 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 [this message]
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
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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