[PATCH AUTOSEL for 4.14 35/67] rtc: ac100: Fix multiple race conditions

Sasha Levin
2018-03-08T04:59:04Z

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 = 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 00000194
pgd = (ptrval)
[00000194] *pgd=00000000
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-dirty #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 = 0x(ptrval))
Stack: (0xee9c9f28 to 0xee9ca000)
9f20: 00000000 7c2fd1be c015ed18 ee9adf40 ee9c0400 ee9c0400
9f40: ee9adf40 c015ed34 ee9c8000 ee9adf64 ee9c0400 c015f040 ee9adf80 00000000
9f60: c015ee24 7c2fd1be ee9adfc0 ee9adf80 00000000 ee9c8000 ee9adf40 c015eef4
9f80: ef1eba34 c0138f14 ee9c8000 ee9adf80 c0138df4 00000000 00000000 00000000
9fa0: 00000000 00000000 00000000 c01010e8 00000000 00000000 00000000 00000000
9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ffffffff ffffffff
[<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 *pdev)
return chip->irq;
}

+ chip->rtc = devm_rtc_allocate_device(&pdev->dev);
+ if (IS_ERR(chip->rtc))
+ return PTR_ERR(chip->rtc);
+
+ chip->rtc->ops = &ac100_rtc_ops;
+
ret = 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 *pdev)
/* clear counter alarm pending interrupts */
regmap_write(chip->regmap, AC100_ALM_INT_STA, AC100_ALM_INT_ENABLE);

- chip->rtc = 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 = ac100_rtc_register_clks(chip);
if (ret)
return ret;

+ ret = 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");

return 0;
--
2.14.1