On Fri, Feb 05, 2021 at 12:50:42AM +0100, Lino Sanfilippo wrote:
From: Lino Sanfilippo l.sanfilippo@kunbus.com
The following sequence of operations results in a refcount warning:
- Open device /dev/tpmrm
- Remove module tpm_tis_spi
- Write a TPM command to the file descriptor opened at step 1.
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
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 removing the flag condition.
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; @@ -261,6 +262,7 @@ void tpm_common_release(struct file *file, struct file_priv *priv) flush_work(&priv->timeout_work); file->private_data = NULL; priv->response_length = 0; + put_device(&chip->dev); }
int __init tpm_dev_common_init(void)
Fix this also by installing an action handler that puts chip->devs as soon as the chip is unregistered.
Fixes: fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm<n>") Fixes: 8979b02aaf1d ("tpm: Fix reference count to main device") Signed-off-by: Lino Sanfilippo l.sanfilippo@kunbus.com drivers/char/tpm/tpm-chip.c | 18 +++++++++++++++--- drivers/char/tpm/tpm_ftpm_tee.c | 2 ++ drivers/char/tpm/tpm_vtpm_proxy.c | 1 + 3 files changed, 18 insertions(+), 3 deletions(-)
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);
This isn't right read what 'or_reset' does
Jason