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Message-ID: <20210615091410.17007-1-vincent.whitchurch@axis.com>
Date: Tue, 15 Jun 2021 11:14:08 +0200
From: Vincent Whitchurch <vincent.whitchurch@...s.com>
To: Peter Huewe <peterhuewe@....de>,
Jarkko Sakkinen <jarkko@...nel.org>,
Jason Gunthorpe <jgg@...pe.ca>,
Stefan Berger <stefanb@...ux.vnet.ibm.com>
CC: <kernel@...s.com>,
Vincent Whitchurch <vincent.whitchurch@...s.com>,
<linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] tpm: Fix tpmrm reference counting
The code added by commit 8979b02aaf1d6de8 ("tpm: Fix reference count to
main device") tries to take an extra reference to the main device only
for TPM2 by looking at the flags, but the flags are actually not set
at the time when tpm_chip_alloc() is called, so no extra reference is
ever taken, leading to a use-after-free if the TPM modules are removed
when the tpmrm device is in use.
==================================================================
BUG: KASAN: use-after-free in __mutex_lock+0xe0/0xbd0
Read of size 8 at addr ffff888116c6acc0 by task sh/1210
CPU: 0 PID: 1210 Comm: sh Not tainted 5.13.0-rc5+ #200
Call Trace:
__mutex_lock+0xe0/0xbd0
tpm2_del_space+0x24/0xa0 [tpm]
tpmrm_release+0x3f/0x50 [tpm]
__fput+0x110/0x3c0
task_work_run+0x94/0xd0
do_exit+0x683/0x13e0
do_syscall_64+0x3c/0x80
Allocated by task 1153:
kasan_save_stack+0x19/0x40
__kasan_kmalloc+0x7f/0xa0
tpm_chip_alloc+0x3b/0x360 [tpm]
tpmm_chip_alloc+0x11/0x70 [tpm]
tpm_tis_core_init+0xce/0x570 [tpm_tis_core]
pnp_device_probe+0x9c/0x100
...
Freed by task 1243:
kfree+0x121/0x340
device_release+0x59/0xf0
kobject_put+0xa5/0x120
release_nodes+0x37f/0x3f0
driver_detach+0x7c/0xf0
bus_remove_driver+0x86/0x110
__x64_sys_delete_module+0x27b/0x320
...
==================================================================
The real fix to the problem which that commit tried to solve is to make
tpmm_chip_alloc() put the ->devs device in the devm release function,
since that is never done anywhere currently. This is safe since
device_initialize() is always called on ->devs. No conditional
reference taking is needed.
Fixes: 8979b02aaf1d6de8 ("tpm: Fix reference count to main device")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
---
drivers/char/tpm/tpm-chip.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index ddaeceb7e109..029ee61c38de 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -358,10 +358,9 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
/* 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)
+ * is in the tpm_devs_release
*/
- 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);
@@ -402,6 +401,14 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
}
EXPORT_SYMBOL_GPL(tpm_chip_alloc);
+static void tpmm_chip_release(void *data)
+{
+ struct tpm_chip *chip = data;
+
+ put_device(&chip->devs);
+ put_device(&chip->dev);
+}
+
/**
* tpmm_chip_alloc() - allocate a new struct tpm_chip instance
* @pdev: parent device to which the chip is associated
@@ -419,9 +426,7 @@ struct tpm_chip *tpmm_chip_alloc(struct device *pdev,
if (IS_ERR(chip))
return chip;
- rc = devm_add_action_or_reset(pdev,
- (void (*)(void *)) put_device,
- &chip->dev);
+ rc = devm_add_action_or_reset(pdev, tpmm_chip_release, chip);
if (rc)
return ERR_PTR(rc);
--
2.28.0
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