Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Alexandre Belloni <alexandre.belloni@free-electrons.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.14 35/67] rtc: ac100: Fix multiple race
 conditions
Thread-Topic: [PATCH AUTOSEL for 4.14 35/67] rtc: ac100: Fix multiple race
 conditions
Thread-Index: AQHTtpoAPaMm9JHUoEyrk+Hr3yY26Q==
Date:   Thu, 8 Mar 2018 04:57:46 +0000
Message-ID: <20180308045641.7814-35-alexander.levin@microsoft.com>
References: <20180308045641.7814-1-alexander.levin@microsoft.com>
In-Reply-To: <20180308045641.7814-1-alexander.levin@microsoft.com>
Accept-Language: en-US
Content-Language: en-US
received-spf: None (protection.outlook.com: microsoft.com does not designate
 permitted sender hosts)
spamdiagnosticoutput: 1:99
spamdiagnosticmetadata: NSPM
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: 37093c68-977c-4fd6-8992-08d584b14b44
X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Mar 2018 04:57:46.8545
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB1015
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

From: Alexandre Belloni <alexandre.belloni@free-electrons.com>

[ Upstream commit 994ec64c0a193940be7a6fd074668b9446d3b6c3 ]

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 =3D 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* */

Also, the interrupt handler: ac100_rtc_irq() is dereferencing chip->rtc but
this may still be NULL when it is called, resulting in:
Unable to handle kernel NULL pointer dereference at virtual address 0000019=
4
pgd =3D (ptrval)
[00000194] *pgd=3D00000000
Internal error: Oops: 5 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 72 Comm: irq/71-ac100-rt Not tainted 4.15.0-rc1-next-20171201-d=
irty #120
Hardware name: Allwinner sun8i Family
task: (ptrval) task.stack: (ptrval)
PC is at mutex_lock+0x14/0x3c
LR is at ac100_rtc_irq+0x38/0xc8
pc : [<c06543a4>]    lr : [<c04d9a2c>]    psr: 60000053
sp : ee9c9f28  ip : 00000000  fp : ee9adfdc
r10: 00000000  r9 : c0a04c48  r8 : c015ed18
r7 : ee9bd600  r6 : ee9c9f28  r5 : ee9af590  r4 : c0a04c48
r3 : ef3cb3c0  r2 : 00000000  r1 : ee9af590  r0 : 00000194
Flags: nZCv  IRQs on  FIQs off  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 4000406a  DAC: 00000051
Process irq/71-ac100-rt (pid: 72, stack limit =3D 0x(ptrval))
Stack: (0xee9c9f28 to 0xee9ca000)
9f20:                   00000000 7c2fd1be c015ed18 ee9adf40 ee9c0400 ee9c04=
00
9f40: ee9adf40 c015ed34 ee9c8000 ee9adf64 ee9c0400 c015f040 ee9adf80 000000=
00
9f60: c015ee24 7c2fd1be ee9adfc0 ee9adf80 00000000 ee9c8000 ee9adf40 c015ee=
f4
9f80: ef1eba34 c0138f14 ee9c8000 ee9adf80 c0138df4 00000000 00000000 000000=
00
9fa0: 00000000 00000000 00000000 c01010e8 00000000 00000000 00000000 000000=
00
9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 000000=
00
9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ffffffff ffffff=
ff
[<c06543a4>] (mutex_lock) from [<c04d9a2c>] (ac100_rtc_irq+0x38/0xc8)
[<c04d9a2c>] (ac100_rtc_irq) from [<c015ed34>] (irq_thread_fn+0x1c/0x54)
[<c015ed34>] (irq_thread_fn) from [<c015f040>] (irq_thread+0x14c/0x214)
[<c015f040>] (irq_thread) from [<c0138f14>] (kthread+0x120/0x150)
[<c0138f14>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)

Solve both issues by moving to
devm_rtc_allocate_device()/rtc_register_device()

Reported-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Tested-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 drivers/rtc/rtc-ac100.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/rtc/rtc-ac100.c b/drivers/rtc/rtc-ac100.c
index 9e336184491c..0e358d4b6738 100644
--- a/drivers/rtc/rtc-ac100.c
+++ b/drivers/rtc/rtc-ac100.c
@@ -567,6 +567,12 @@ static int ac100_rtc_probe(struct platform_device *pde=
v)
 		return chip->irq;
 	}
=20
+	chip->rtc =3D devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(chip->rtc))
+		return PTR_ERR(chip->rtc);
+
+	chip->rtc->ops =3D &ac100_rtc_ops;
+
 	ret =3D devm_request_threaded_irq(&pdev->dev, chip->irq, NULL,
 					ac100_rtc_irq,
 					IRQF_SHARED | IRQF_ONESHOT,
@@ -586,17 +592,16 @@ static int ac100_rtc_probe(struct platform_device *pd=
ev)
 	/* clear counter alarm pending interrupts */
 	regmap_write(chip->regmap, AC100_ALM_INT_STA, AC100_ALM_INT_ENABLE);
=20
-	chip->rtc =3D devm_rtc_device_register(&pdev->dev, "rtc-ac100",
-					     &ac100_rtc_ops, THIS_MODULE);
-	if (IS_ERR(chip->rtc)) {
-		dev_err(&pdev->dev, "unable to register device\n");
-		return PTR_ERR(chip->rtc);
-	}
-
 	ret =3D ac100_rtc_register_clks(chip);
 	if (ret)
 		return ret;
=20
+	ret =3D rtc_register_device(chip->rtc);
+	if (ret) {
+		dev_err(&pdev->dev, "unable to register device\n");
+		return ret;
+	}
+
 	dev_info(&pdev->dev, "RTC enabled\n");
=20
 	return 0;
--=20
2.14.1