Re: [PATCH v6] tpm: fix reference counting for struct tpm_chip

On Fri, Feb 19, 2021 at 11:13:45AM +0200, Jarkko Sakkinen wrote:

On Thu, Feb 18, 2021 at 09:29:41PM +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 Signed-off-by: Jason Gunthorpe jgg@ziepe.ca Signed-off-by: Lino Sanfilippo l.sanfilippo@kunbus.com

---

drivers/char/tpm/tpm-chip.c | 48 ++++++++----------------------------- drivers/char/tpm/tpm.h | 1 + drivers/char/tpm/tpm2-space.c | 55 +++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 66 insertions(+), 38 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c index ddaeceb..ae6e414 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; @@ -352,39 +343,20 @@ 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;
  

if (!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) {

• 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 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;

+del_cdev:

• cdev_device_del(&chip->cdev, &chip->dev); return rc;

} @@ -640,8 +610,10 @@ void tpm_chip_unregister(struct tpm_chip *chip) if (IS_ENABLED(CONFIG_HW_RANDOM_TPM)) hwrng_unregister(&chip->hwrng); tpm_bios_log_teardown(chip);

• if (chip->flags & TPM_CHIP_FLAG_TPM2)

• if (chip->flags & TPM_CHIP_FLAG_TPM2) { cdev_device_del(&chip->cdevs, &chip->devs);

• put_device(&chip->devs);
  

• } 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 947d1db..ac4b2dc 100644 --- a/drivers/char/tpm/tpm.h +++ b/drivers/char/tpm/tpm.h @@ -238,6 +238,7 @@ 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_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 784b8b3..6d17f77 100644 --- a/drivers/char/tpm/tpm2-space.c +++ b/drivers/char/tpm/tpm2-space.c @@ -571,3 +571,58 @@ 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);

+}

+/*

• • 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 out_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 out_put_devs;
  

• }
• return 0;

+out_put_devs:

A nit:

1. You have already del_cdev:
2. Here you use a differing convention with out prefix.

I'd suggest that you put err_ to both:

1. err_del_cdev
2. err_put_devs

It's quite coherent what we have already:

linux-tpmdd on  next took 8s ❯ git grep "^err_.*" drivers/char/tpm/ | wc -l 17

I guess there's some ambiguity with this, but IMHO makes a lot of sense for code blocks *only* executed as an exception handler.

/Jarkko