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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.16 157/161] rtc: rk808: fix possible race condition
Date:   Thu, 24 May 2018 11:39:42 +0200
Message-Id: <20180524093037.019031273@linuxfoundation.org>
In-Reply-To: <20180524093018.331893860@linuxfoundation.org>
References: <20180524093018.331893860@linuxfoundation.org>
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4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexandre Belloni <alexandre.belloni@bootlin.com>

[ Upstream commit 201fac95e799c3d0304ec724d555e1251b9f6e84 ]

The probe function is not allowed to fail after registering the RTC because
the following may happen:

CPU0:                                CPU1:
sys_load_module()
 do_init_module()
  do_one_initcall()
   cmos_do_probe()
    rtc_device_register()
     __register_chrdev()
     cdev->owner = struct module*
                                     open("/dev/rtc0")
    rtc_device_unregister()
  module_put()
  free_module()
   module_free(mod->module_core)
   /* struct module *module is now
      freed */
                                      chrdev_open()
                                       spin_lock(cdev_lock)
                                       cdev_get()
                                        try_module_get()
                                         module_is_live()
                                         /* dereferences already
                                            freed struct module* */

Switch to devm_rtc_allocate_device/rtc_register_device to register the rtc
as late as possible.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/rtc/rtc-rk808.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/drivers/rtc/rtc-rk808.c
+++ b/drivers/rtc/rtc-rk808.c
@@ -416,12 +416,11 @@ static int rk808_rtc_probe(struct platfo
 
 	device_init_wakeup(&pdev->dev, 1);
 
-	rk808_rtc->rtc = devm_rtc_device_register(&pdev->dev, "rk808-rtc",
-						  &rk808_rtc_ops, THIS_MODULE);
-	if (IS_ERR(rk808_rtc->rtc)) {
-		ret = PTR_ERR(rk808_rtc->rtc);
-		return ret;
-	}
+	rk808_rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rk808_rtc->rtc))
+		return PTR_ERR(rk808_rtc->rtc);
+
+	rk808_rtc->rtc->ops = &rk808_rtc_ops;
 
 	rk808_rtc->irq = platform_get_irq(pdev, 0);
 	if (rk808_rtc->irq < 0) {
@@ -438,9 +437,10 @@ static int rk808_rtc_probe(struct platfo
 	if (ret) {
 		dev_err(&pdev->dev, "Failed to request alarm IRQ %d: %d\n",
 			rk808_rtc->irq, ret);
+		return ret;
 	}
 
-	return ret;
+	return rtc_register_device(rk808_rtc->rtc);
 }
 
 static struct platform_driver rk808_rtc_driver = {