[PATCH] memstick: rtsx_usb_ms: fix UAF

[Tong Zhang]

This patch fixes the following issues:
1. memstick_free_host() will free the host, so the use of ms_dev(host) after
it will be a problem. To fix this, move memstick_free_host() after when we
are done with ms_dev(host).
2. if something bad happens in memstick_add_host() and we end up taking
err_out in rtsx_usb_ms_drv_probe(), we'd better avoid running rtsx_usb_ms_drv_remove()
3. In rtsx_usb_ms_drv_remove(), pm need to be disabled before we remove
and free host otherwise memstick_check will be called and UAF will
happen.

[   11.351173] BUG: KASAN: use-after-free in rtsx_usb_ms_drv_remove+0x94/0x140 [rtsx_usb_ms]
[   11.357077]  rtsx_usb_ms_drv_remove+0x94/0x140 [rtsx_usb_ms]
[   11.357376]  platform_remove+0x2a/0x50
[   11.367531] Freed by task 298:
[   11.368537]  kfree+0xa4/0x2a0
[   11.368711]  device_release+0x51/0xe0
[   11.368905]  kobject_put+0xa2/0x120
[   11.369090]  rtsx_usb_ms_drv_remove+0x8c/0x140 [rtsx_usb_ms]
[   11.369386]  platform_remove+0x2a/0x50

[   12.038408] BUG: KASAN: use-after-free in __mutex_lock.isra.0+0x3ec/0x7c0
[   12.045432]  mutex_lock+0xc9/0xd0
[   12.046080]  memstick_check+0x6a/0x578 [memstick]
[   12.046509]  process_one_work+0x46d/0x750
[   12.052107] Freed by task 297:
[   12.053115]  kfree+0xa4/0x2a0
[   12.053272]  device_release+0x51/0xe0
[   12.053463]  kobject_put+0xa2/0x120
[   12.053647]  rtsx_usb_ms_drv_remove+0xc4/0x140 [rtsx_usb_ms]
[   12.053939]  platform_remove+0x2a/0x50

Signed-off-by: Tong Zhang <ztong0001@xxxxxxxxx>
---
 drivers/memstick/host/rtsx_usb_ms.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/memstick/host/rtsx_usb_ms.c b/drivers/memstick/host/rtsx_usb_ms.c
index 102dbb8080da..851643d007b7 100644
--- a/drivers/memstick/host/rtsx_usb_ms.c
+++ b/drivers/memstick/host/rtsx_usb_ms.c
@@ -799,9 +799,10 @@ static int rtsx_usb_ms_drv_probe(struct platform_device *pdev)
 
 	return 0;
 err_out:
-	memstick_free_host(msh);
 	pm_runtime_disable(ms_dev(host));
 	pm_runtime_put_noidle(ms_dev(host));
+	memstick_free_host(msh);
+	platform_set_drvdata(pdev, NULL);
 	return err;
 }
 
@@ -811,6 +812,8 @@ static int rtsx_usb_ms_drv_remove(struct platform_device *pdev)
 	struct memstick_host *msh = host->msh;
 	int err;
 
+	if (!host)
+		return 0;
 	host->eject = true;
 	cancel_work_sync(&host->handle_req);
 
@@ -828,9 +831,6 @@ static int rtsx_usb_ms_drv_remove(struct platform_device *pdev)
 	}
 	mutex_unlock(&host->host_mutex);
 
-	memstick_remove_host(msh);
-	memstick_free_host(msh);
-
 	/* Balance possible unbalanced usage count
 	 * e.g. unconditional module removal
 	 */
@@ -838,10 +838,11 @@ static int rtsx_usb_ms_drv_remove(struct platform_device *pdev)
 		pm_runtime_put(ms_dev(host));
 
 	pm_runtime_disable(ms_dev(host));
-	platform_set_drvdata(pdev, NULL);
-
+	memstick_remove_host(msh);
 	dev_dbg(ms_dev(host),
 		": Realtek USB Memstick controller has been removed\n");
+	memstick_free_host(msh);
+	platform_set_drvdata(pdev, NULL);
 
 	return 0;
 }
-- 
2.25.1