linux-kernel - [PATCH v2] char: tpm: vtpm

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Date:   Thu,  8 Jul 2021 15:22:59 +0530
From:   Saubhik Mukherjee <saubhik.mukherjee@...il.com>
To:     peterhuewe@....de, jarkko@...nel.org, jgg@...pe.ca
Cc:     Saubhik Mukherjee <saubhik.mukherjee@...il.com>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        ldv-project@...uxtesting.org, andrianov@...ras.ru
Subject: [PATCH v2] char: tpm: vtpm_proxy: Fix race in init

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@...il.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