[PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip

[Lino Sanfilippo]

From: Lino Sanfilippo <l.sanfilippo@xxxxxxxxxx>

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 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.

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@xxxxxxxxxx>
---
 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
--- a/drivers/char/tpm/tpm-chip.c
+++ 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);
+	}
+
+	rc = devm_add_action_or_reset(pdev,
+				      (void (*)(void *)) put_device,
+				      &chip->devs);
+	if (rc) {
+		devm_remove_action(pdev,
+				   (void (*)(void *)) put_device,
+				   &chip->dev);
+		put_device(&chip->dev);
+		return ERR_PTR(rc);
+	}
 
 	dev_set_drvdata(pdev, chip);
 
diff --git a/drivers/char/tpm/tpm_ftpm_tee.c b/drivers/char/tpm/tpm_ftpm_tee.c
index 2ccdf8a..82858c2 100644
--- a/drivers/char/tpm/tpm_ftpm_tee.c
+++ b/drivers/char/tpm/tpm_ftpm_tee.c
@@ -286,6 +286,7 @@ static int ftpm_tee_probe(struct device *dev)
 
 out_chip:
 	put_device(&pvt_data->chip->dev);
+	put_device(&pvt_data->chip->devs);
 out_chip_alloc:
 	tee_shm_free(pvt_data->shm);
 out_shm_alloc:
@@ -318,6 +319,7 @@ static int ftpm_tee_remove(struct device *dev)
 	tpm_chip_unregister(pvt_data->chip);
 
 	/* frees chip */
+	put_device(&pvt_data->chip->devs);
 	put_device(&pvt_data->chip->dev);
 
 	/* Free the shared memory pool */
diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
index 91c772e3..97b60f8 100644
--- a/drivers/char/tpm/tpm_vtpm_proxy.c
+++ b/drivers/char/tpm/tpm_vtpm_proxy.c
@@ -520,6 +520,7 @@ static struct proxy_dev *vtpm_proxy_create_proxy_dev(void)
  */
 static inline void vtpm_proxy_delete_proxy_dev(struct proxy_dev *proxy_dev)
 {
+	put_device(&proxy_dev->chip->devs);
 	put_device(&proxy_dev->chip->dev); /* frees chip */
 	kfree(proxy_dev);
 }
-- 
2.7.4