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

> + put_device(&chip->devs);
> +
> + return rc;
> +}
> --
> 2.7.4
>

Other than that, no complains.

/Jarkko

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