linux-kernel - [PATCH v2] tpm: tpm_vtpm_proxy: fix a race condition in /dev/vtpmx creation

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Date:   Tue, 16 May 2023 01:25:54 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     linux-integrity@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...i.fi>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] tpm: tpm_vtpm_proxy: fix a race condition in /dev/vtpmx creation

From: Jarkko Sakkinen <jarkko.sakkinen@...i.fi>

/dev/vtpmx is made visible before 'workqueue' is initialized, which can
lead to a memory corruption in the worst case scenario.

Address this by initializing 'workqueue' as the very first step of the
driver initialization.

Cc: stable@...r.kernel.org
Fixes: 6f99612e2500 ("tpm: Proxy driver for supporting multiple emulated TPMs")
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...i.fi>
---
v2:
- Replace vtpmx_cleanup() with destroy_workqueue():
  https://lore.kernel.org/linux-integrity/CSLCEYDKKWWE.36POIXVT65SLE@suppilovahvero/
- Fix typo:
  https://lore.kernel.org/linux-integrity/4651cf1c-423d-05c2-b4c3-9d829a2eadf4@linux.ibm.com/
---
 drivers/char/tpm/tpm_vtpm_proxy.c | 30 +++++++-----------------------
 1 file changed, 7 insertions(+), 23 deletions(-)

diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
index 5c865987ba5c..30e953988cab 100644
--- a/drivers/char/tpm/tpm_vtpm_proxy.c
+++ b/drivers/char/tpm/tpm_vtpm_proxy.c
@@ -683,37 +683,21 @@ static struct miscdevice vtpmx_miscdev = {
 	.fops = &vtpmx_fops,
 };
 
-static int vtpmx_init(void)
-{
-	return misc_register(&vtpmx_miscdev);
-}
-
-static void vtpmx_cleanup(void)
-{
-	misc_deregister(&vtpmx_miscdev);
-}
-
 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;
 	}
 
-	return 0;
-
-err_vtpmx_cleanup:
-	vtpmx_cleanup();
+	rc = misc_register(&vtpmx_miscdev);
+	if (rc) {
+		pr_err("couldn't create vtpmx device\n");
+		destroy_workqueue(workqueue);
+	}
 
 	return rc;
 }
@@ -721,7 +705,7 @@ static int __init vtpm_module_init(void)
 static void __exit vtpm_module_exit(void)
 {
 	destroy_workqueue(workqueue);
-	vtpmx_cleanup();
+	misc_deregister(&vtpmx_miscdev);
 }
 
 module_init(vtpm_module_init);
-- 
2.39.2