| Message ID | 20210615091410.17007-1-vincent.whitchurch@axis.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] tpm: Fix tpmrm reference counting | expand |
On Tue, Jun 15, 2021 at 11:14:08AM +0200, Vincent Whitchurch wrote: > 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. Please read this https://lore.kernel.org/linux-integrity/20210205172528.GP4718@ziepe.ca/ Jason
On Wed, Jun 16, 2021 at 08:53:01PM +0200, Jason Gunthorpe wrote: > On Tue, Jun 15, 2021 at 11:14:08AM +0200, Vincent Whitchurch wrote: > > 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. > > Please read this > > https://lore.kernel.org/linux-integrity/20210205172528.GP4718@ziepe.ca/ Thank you for the pointer. I see that Lino already posted your proposal as a real patch as you requested so I will drop this. https://lore.kernel.org/linux-integrity/1613949567-1181-2-git-send-email-LinoSanfilippo@gmx.de/
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);
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@axis.com> --- drivers/char/tpm/tpm-chip.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-)