Re: [PATCH v9 1/1] tpm: fix reference counting for struct tpm_chip

[Stefan Berger <stefanb@linux.ibm.com>]

On 3/3/22 17:45, Jarkko Sakkinen wrote:
> On Wed, Mar 02, 2022 at 10:43:53AM +0100, Lino Sanfilippo wrote:
>> From: Lino Sanfilippo <l.sanfilippo@kunbus.com>
>>
>> The following sequence of operations results in a refcount warning:
>>
>> 1. Open device /dev/tpmrm.
>> 2. Remove module tpm_tis_spi.
>> 3. Write a TPM command to the file descriptor opened at step 1.
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 3 PID: 1161 at lib/refcount.c:25 kobject_get+0xa0/0xa4
>> refcount_t: addition on 0; use-after-free.
>> Modules linked in: tpm_tis_spi tpm_tis_core tpm mdio_bcm_unimac brcmfmac
>> sha256_generic libsha256 sha256_arm hci_uart btbcm bluetooth cfg80211 vc4
>> brcmutil ecdh_generic ecc snd_soc_core crc32_arm_ce libaes
>> raspberrypi_hwmon ac97_bus snd_pcm_dmaengine bcm2711_thermal snd_pcm
>> snd_timer genet snd phy_generic soundcore [last unloaded: spi_bcm2835]
>> CPU: 3 PID: 1161 Comm: hold_open Not tainted 5.10.0ls-main-dirty #2
>> Hardware name: BCM2711
>> [<c0410c3c>] (unwind_backtrace) from [<c040b580>] (show_stack+0x10/0x14)
>> [<c040b580>] (show_stack) from [<c1092174>] (dump_stack+0xc4/0xd8)
>> [<c1092174>] (dump_stack) from [<c0445a30>] (__warn+0x104/0x108)
>> [<c0445a30>] (__warn) from [<c0445aa8>] (warn_slowpath_fmt+0x74/0xb8)
>> [<c0445aa8>] (warn_slowpath_fmt) from [<c08435d0>] (kobject_get+0xa0/0xa4)
>> [<c08435d0>] (kobject_get) from [<bf0a715c>] (tpm_try_get_ops+0x14/0x54 [tpm])
>> [<bf0a715c>] (tpm_try_get_ops [tpm]) from [<bf0a7d6c>] (tpm_common_write+0x38/0x60 [tpm])
>> [<bf0a7d6c>] (tpm_common_write [tpm]) from [<c05a7ac0>] (vfs_write+0xc4/0x3c0)
>> [<c05a7ac0>] (vfs_write) from [<c05a7ee4>] (ksys_write+0x58/0xcc)
>> [<c05a7ee4>] (ksys_write) from [<c04001a0>] (ret_fast_syscall+0x0/0x4c)
>> Exception stack(0xc226bfa8 to 0xc226bff0)
>> bfa0:                   00000000 000105b4 00000003 beafe664 00000014 00000000
>> bfc0: 00000000 000105b4 000103f8 00000004 00000000 00000000 b6f9c000 beafe684
>> bfe0: 0000006c beafe648 0001056c b6eb6944
>> ---[ end trace d4b8409def9b8b1f ]---
>>
>> The reason for this warning is the attempt to get the chip->dev reference
>> in tpm_common_write() although the reference counter is already zero.
>>
>> Since commit 8979b02aaf1d ("tpm: Fix reference count to main device") the
>> extra reference used to prevent a premature zero counter is never taken,
>> because the required TPM_CHIP_FLAG_TPM2 flag is never set.
>>
>> Fix this by moving the TPM 2 character device handling from
>> tpm_chip_alloc() to tpm_add_char_device() which is called at a later point
>> in time when the flag has been set in case of TPM2.
>>
>> 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.
>>
>> Fix this by putting chip->devs in tpm_chip_unregister().
>>
>> Finally move the new implementation for the TPM 2 handling into a new
>> function to avoid multiple checks for the TPM_CHIP_FLAG_TPM2 flag in the
>> good case and error cases.
>>
>> Cc: stable@vger.kernel.org
>> Fixes: fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm<n>")
>> Fixes: 8979b02aaf1d ("tpm: Fix reference count to main device")
>> Co-developed-by: Jason Gunthorpe <jgg@ziepe.ca>
>> Tested-by: Stefan Berger <stefanb@linux.ibm.com>
>> Signed-off-by: Jason Gunthorpe <jgg@ziepe.ca>
>> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
>> ---
>>   drivers/char/tpm/tpm-chip.c   | 46 +++++--------------------
>>   drivers/char/tpm/tpm.h        |  2 ++
>>   drivers/char/tpm/tpm2-space.c | 65 +++++++++++++++++++++++++++++++++++
>>   3 files changed, 75 insertions(+), 38 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>> index b009e7479b70..783d65fc71f0 100644
>> --- a/drivers/char/tpm/tpm-chip.c
>> +++ b/drivers/char/tpm/tpm-chip.c
>> @@ -274,14 +274,6 @@ static void tpm_dev_release(struct device *dev)
>>   	kfree(chip);
>>   }
>>   
>> -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);
>> -}
>> -
>>   /**
>>    * tpm_class_shutdown() - prepare the TPM device for loss of power.
>>    * @dev: device to which the chip is associated.
>> @@ -344,7 +336,6 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>>   	chip->dev_num = rc;
>>   
>>   	device_initialize(&chip->dev);
>> -	device_initialize(&chip->devs);
>>   
>>   	chip->dev.class = tpm_class;
>>   	chip->dev.class->shutdown_pre = tpm_class_shutdown;
>> @@ -352,29 +343,12 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>>   	chip->dev.parent = pdev;
>>   	chip->dev.groups = chip->groups;
>>   
>> -	chip->devs.parent = pdev;
>> -	chip->devs.class = tpmrm_class;
>> -	chip->devs.release = tpm_devs_release;
>> -	/* get extra reference on main device to hold on
>> -	 * behalf of devs.  This holds the chip structure
>> -	 * 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);
>> -
>>   	if (chip->dev_num == 0)
>>   		chip->dev.devt = MKDEV(MISC_MAJOR, TPM_MINOR);
>>   	else
>>   		chip->dev.devt = MKDEV(MAJOR(tpm_devt), chip->dev_num);
>>   
>> -	chip->devs.devt =
>> -		MKDEV(MAJOR(tpm_devt), chip->dev_num + TPM_NUM_DEVICES);
>> -
>>   	rc = dev_set_name(&chip->dev, "tpm%d", chip->dev_num);
>> -	if (rc)
>> -		goto out;
>> -	rc = dev_set_name(&chip->devs, "tpmrm%d", chip->dev_num);
>>   	if (rc)
>>   		goto out;
>>   
>> @@ -382,9 +356,7 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>>   		chip->flags |= TPM_CHIP_FLAG_VIRTUAL;
>>   
>>   	cdev_init(&chip->cdev, &tpm_fops);
>> -	cdev_init(&chip->cdevs, &tpmrm_fops);
>>   	chip->cdev.owner = THIS_MODULE;
>> -	chip->cdevs.owner = THIS_MODULE;
>>   
>>   	rc = tpm2_init_space(&chip->work_space, TPM2_SPACE_BUFFER_SIZE);
>>   	if (rc) {
>> @@ -396,7 +368,6 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>>   	return chip;
>>   
>>   out:
>> -	put_device(&chip->devs);
>>   	put_device(&chip->dev);
>>   	return ERR_PTR(rc);
>>   }
>> @@ -445,14 +416,9 @@ static int tpm_add_char_device(struct tpm_chip *chip)
>>   	}
>>   
>>   	if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip)) {
>> -		rc = cdev_device_add(&chip->cdevs, &chip->devs);
>> -		if (rc) {
>> -			dev_err(&chip->devs,
>> -				"unable to cdev_device_add() %s, major %d, minor %d, err=%d\n",
>> -				dev_name(&chip->devs), MAJOR(chip->devs.devt),
>> -				MINOR(chip->devs.devt), rc);
>> -			return rc;
>> -		}
>> +		rc = tpm_devs_add(chip);
>> +		if (rc)
>> +			goto err_del_cdev;
>>   	}
>>   
>>   	/* Make the chip available. */
>> @@ -460,6 +426,10 @@ static int tpm_add_char_device(struct tpm_chip *chip)
>>   	idr_replace(&dev_nums_idr, chip, chip->dev_num);
>>   	mutex_unlock(&idr_lock);
>>   
>> +	return 0;
>> +
>> +err_del_cdev:
>> +	cdev_device_del(&chip->cdev, &chip->dev);
>>   	return rc;
>>   }
>>   
>> @@ -654,7 +624,7 @@ void tpm_chip_unregister(struct tpm_chip *chip)
>>   		hwrng_unregister(&chip->hwrng);
>>   	tpm_bios_log_teardown(chip);
>>   	if (chip->flags & TPM_CHIP_FLAG_TPM2 && !tpm_is_firmware_upgrade(chip))
>> -		cdev_device_del(&chip->cdevs, &chip->devs);
>> +		tpm_devs_remove(chip);
>>   	tpm_del_char_device(chip);
>>   }
>>   EXPORT_SYMBOL_GPL(tpm_chip_unregister);
>> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
>> index 283f78211c3a..2163c6ee0d36 100644
>> --- a/drivers/char/tpm/tpm.h
>> +++ b/drivers/char/tpm/tpm.h
>> @@ -234,6 +234,8 @@ int tpm2_prepare_space(struct tpm_chip *chip, struct tpm_space *space, u8 *cmd,
>>   		       size_t cmdsiz);
>>   int tpm2_commit_space(struct tpm_chip *chip, struct tpm_space *space, void *buf,
>>   		      size_t *bufsiz);
>> +int tpm_devs_add(struct tpm_chip *chip);
>> +void tpm_devs_remove(struct tpm_chip *chip);
>>   
>>   void tpm_bios_log_setup(struct tpm_chip *chip);
>>   void tpm_bios_log_teardown(struct tpm_chip *chip);
>> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
>> index 97e916856cf3..265ec72b1d81 100644
>> --- a/drivers/char/tpm/tpm2-space.c
>> +++ b/drivers/char/tpm/tpm2-space.c
>> @@ -574,3 +574,68 @@ int tpm2_commit_space(struct tpm_chip *chip, struct tpm_space *space,
>>   	dev_err(&chip->dev, "%s: error %d\n", __func__, rc);
>>   	return rc;
>>   }
>> +
>> +/*
>> + * Put the reference to the main device.
>> + */
>> +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);
>> +}
>> +
>> +/*
>> + * Remove the device file for exposed TPM spaces and release the device
>> + * reference. This may also release the reference to the master device.
>> + */
>> +void tpm_devs_remove(struct tpm_chip *chip)
>> +{
>> +	cdev_device_del(&chip->cdevs, &chip->devs);
>> +	put_device(&chip->devs);
>> +}
>> +
>> +/*
>> + * Add a device file to expose TPM spaces. Also take a reference to the
>> + * main device.
>> + */
>> +int tpm_devs_add(struct tpm_chip *chip)
>> +{
>> +	int rc;
>> +
>> +	device_initialize(&chip->devs);
>> +	chip->devs.parent = chip->dev.parent;
>> +	chip->devs.class = tpmrm_class;
>> +
>> +	/*
>> +	 * Get extra reference on main device to hold on behalf of devs.
>> +	 * This holds the chip structure while cdevs is in use. The
>> +	 * corresponding put is in the tpm_devs_release.
>> +	 */
>> +	get_device(&chip->dev);
>> +	chip->devs.release = tpm_devs_release;
>> +	chip->devs.devt = MKDEV(MAJOR(tpm_devt), chip->dev_num + TPM_NUM_DEVICES);
>> +	cdev_init(&chip->cdevs, &tpmrm_fops);
>> +	chip->cdevs.owner = THIS_MODULE;
>> +
>> +	rc = dev_set_name(&chip->devs, "tpmrm%d", chip->dev_num);
>> +	if (rc)
>> +		goto err_put_devs;
>> +
>> +	rc = cdev_device_add(&chip->cdevs, &chip->devs);
>> +	if (rc) {
>> +		dev_err(&chip->devs,
>> +			"unable to cdev_device_add() %s, major %d, minor %d, err=%d\n",
>> +			dev_name(&chip->devs), MAJOR(chip->devs.devt),
>> +			MINOR(chip->devs.devt), rc);
>> +		goto err_put_devs;
>> +	}
>> +
>> +	return 0;
>> +
>> +err_put_devs:
>> +	put_device(&chip->devs);
>> +
>> +	return rc;
>> +}
>> -- 
>> 2.35.1
>>
> LGTM, thank you.
>
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
>
> Stefan, if possible, for sanity check, redo test with v9.

We need that other patch as well!


Tested-by: Stefan Berger <stefanb@linux.ibm.com>




    Stefan

>
> BR, Jarkko