[PATCH v2] char: tpm: vtpm_proxy: Fix race in init

[PATCH v2] char: tpm: vtpm_proxy: Fix race in init

[Saubhik Mukherjee]

vtpm_module_init calls vtpmx_init which calls misc_register. The file
operations callbacks are registered. So, vtpmx_fops_ioctl can execute in
parallel with rest of vtpm_module_init. vtpmx_fops_ioctl calls
vtpmx_ioc_new_dev, which calls vtpm_proxy_create_device, which calls
vtpm_proxy_work_start, which could read uninitialized workqueue.

To avoid this, create workqueue before vtpmx init.

Found by Linux Driver Verification project (linuxtesting.org).

Fixes: 6f99612e2500 ("tpm: Proxy driver for supporting multiple emulated TPMs")
Signed-off-by: Saubhik Mukherjee <saubhik.mukherjee@gmail.com>
---

Changes since v1 ([0]):
- Add Fixes tag to commit message, as requested by Jarkko in [1].

[0]: https://lkml.org/lkml/2021/6/23/572
[1]: https://lkml.org/lkml/2021/6/29/695

 drivers/char/tpm/tpm_vtpm_proxy.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
index 91c772e38bb5..225dfa026a8f 100644
--- a/drivers/char/tpm/tpm_vtpm_proxy.c
+++ b/drivers/char/tpm/tpm_vtpm_proxy.c
@@ -697,23 +697,22 @@ static int __init vtpm_module_init(void)
 {
 	int rc;
 
-	rc = vtpmx_init();
-	if (rc) {
-		pr_err("couldn't create vtpmx device\n");
-		return rc;
-	}
-
 	workqueue = create_workqueue("tpm-vtpm");
 	if (!workqueue) {
 		pr_err("couldn't create workqueue\n");
-		rc = -ENOMEM;
-		goto err_vtpmx_cleanup;
+		return -ENOMEM;
+	}
+
+	rc = vtpmx_init();
+	if (rc) {
+		pr_err("couldn't create vtpmx device\n");
+		goto err_destroy_workqueue;
 	}
 
 	return 0;
 
-err_vtpmx_cleanup:
-	vtpmx_cleanup();
+err_destroy_workqueue:
+	destroy_workqueue(workqueue);
 
 	return rc;
 }
-- 
2.30.2

Re: [PATCH v2] char: tpm: vtpm_proxy: Fix race in init

[Jarkko Sakkinen]

On Thu, Jul 08, 2021 at 03:22:59PM +0530, Saubhik Mukherjee wrote:
> vtpm_module_init calls vtpmx_init which calls misc_register. The file
> operations callbacks are registered. So, vtpmx_fops_ioctl can execute in
> parallel with rest of vtpm_module_init. vtpmx_fops_ioctl calls
> vtpmx_ioc_new_dev, which calls vtpm_proxy_create_device, which calls
> vtpm_proxy_work_start, which could read uninitialized workqueue.
> 
> To avoid this, create workqueue before vtpmx init.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Fixes: 6f99612e2500 ("tpm: Proxy driver for supporting multiple emulated TPMs")
> Signed-off-by: Saubhik Mukherjee <saubhik.mukherjee@gmail.com>
> ---
> 
> Changes since v1 ([0]):
> - Add Fixes tag to commit message, as requested by Jarkko in [1].
> 
> [0]: https://lkml.org/lkml/2021/6/23/572
> [1]: https://lkml.org/lkml/2021/6/29/695
> 
>  drivers/char/tpm/tpm_vtpm_proxy.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
> index 91c772e38bb5..225dfa026a8f 100644
> --- a/drivers/char/tpm/tpm_vtpm_proxy.c
> +++ b/drivers/char/tpm/tpm_vtpm_proxy.c
> @@ -697,23 +697,22 @@ static int __init vtpm_module_init(void)
>  {
>  	int rc;
>  
> -	rc = vtpmx_init();
> -	if (rc) {
> -		pr_err("couldn't create vtpmx device\n");
> -		return rc;
> -	}
> -
>  	workqueue = create_workqueue("tpm-vtpm");
>  	if (!workqueue) {
>  		pr_err("couldn't create workqueue\n");
> -		rc = -ENOMEM;
> -		goto err_vtpmx_cleanup;
> +		return -ENOMEM;
> +	}
> +
> +	rc = vtpmx_init();
> +	if (rc) {
> +		pr_err("couldn't create vtpmx device\n");
> +		goto err_destroy_workqueue;
>  	}
>  
>  	return 0;
>  
> -err_vtpmx_cleanup:
> -	vtpmx_cleanup();
> +err_destroy_workqueue:
> +	destroy_workqueue(workqueue);
>  
>  	return rc;
>  }
> -- 
> 2.30.2
> 
> 

Thanks, I applied this.

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

/Jarkko

Re: [PATCH v2] char: tpm: vtpm_proxy: Fix race in init

[Stefan Berger]

On 7/8/21 5:52 AM, Saubhik Mukherjee wrote:
> vtpm_module_init calls vtpmx_init which calls misc_register. The file
> operations callbacks are registered. So, vtpmx_fops_ioctl can execute in
> parallel with rest of vtpm_module_init. vtpmx_fops_ioctl calls
> vtpmx_ioc_new_dev, which calls vtpm_proxy_create_device, which calls
> vtpm_proxy_work_start, which could read uninitialized workqueue.
>
> To avoid this, create workqueue before vtpmx init.
>
> Found by Linux Driver Verification project (linuxtesting.org).
>
> Fixes: 6f99612e2500 ("tpm: Proxy driver for supporting multiple emulated TPMs")
> Signed-off-by: Saubhik Mukherjee <saubhik.mukherjee@gmail.com>

Tested-by: Stefan Berger <stefanb@linux.ibm.com>