2021-10-11 16:27:43

by Yang Yingliang

Subject: [PATCH] rtc: class: don't call cdev_device_del() when cdev_device_add() failed

I got a null-ptr-deref report when doing fault injection test:

general protection fault, probably for non-canonical address 0xdffffc0000000022: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000110-0x0000000000000117]
RIP: 0010:device_del+0x132/0xdc0
Call Trace:
cdev_device_del+0x1a/0x80
devm_rtc_unregister_device+0x37/0x80
release_nodes+0xc3/0x3b0

If cdev_device_add() fails, 'dev->p' is not set, it causes
null-ptr-deref when calling cdev_device_del(). Registering
character device is optional, we don't return error code
here, so introduce a new flag 'RTC_NO_CDEV' to indicate
if it has character device, cdev_device_del() is called
when this bit is not set.

Reported-by: Hulk Robot <[email protected]>
Signed-off-by: Yang Yingliang <[email protected]>
---
drivers/rtc/class.c | 9 ++++++---
include/linux/rtc.h | 1 +
2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 1f18c39a4b82..dbccd71589b9 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -334,7 +334,8 @@ static void devm_rtc_unregister_device(void *data)
* letting any rtc_class_open() users access it again
*/
rtc_proc_del_device(rtc);
- cdev_device_del(&rtc->char_dev, &rtc->dev);
+ if (!test_bit(RTC_NO_CDEV, &rtc->flags))
+ cdev_device_del(&rtc->char_dev, &rtc->dev);
rtc->ops = NULL;
mutex_unlock(&rtc->ops_lock);
}
@@ -399,12 +400,14 @@ int __devm_rtc_register_device(struct module *owner, struct rtc_device *rtc)
rtc_dev_prepare(rtc);

err = cdev_device_add(&rtc->char_dev, &rtc->dev);
- if (err)
+ if (err) {
+ set_bit(RTC_NO_CDEV, &rtc->flags);
dev_warn(rtc->dev.parent, "failed to add char device %d:%d\n",
MAJOR(rtc->dev.devt), rtc->id);
- else
+ } else {
dev_dbg(rtc->dev.parent, "char device (%d:%d)\n",
MAJOR(rtc->dev.devt), rtc->id);
+ }

rtc_proc_add_device(rtc);

diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index bd611e26291d..354e0843ab17 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -80,6 +80,7 @@ struct rtc_timer {

/* flags */
#define RTC_DEV_BUSY 0
+#define RTC_NO_CDEV 1

struct rtc_device {
struct device dev;
--
2.25.1

2021-10-17 20:36:45

by Alexandre Belloni

Subject: Re: [PATCH] rtc: class: don't call cdev_device_del() when cdev_device_add() failed

On Mon, 11 Oct 2021 21:21:14 +0800, Yang Yingliang wrote:
> I got a null-ptr-deref report when doing fault injection test:
>
> general protection fault, probably for non-canonical address 0xdffffc0000000022: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x0000000000000110-0x0000000000000117]
> RIP: 0010:device_del+0x132/0xdc0
> Call Trace:
> cdev_device_del+0x1a/0x80
> devm_rtc_unregister_device+0x37/0x80
> release_nodes+0xc3/0x3b0
>
> [...]

Applied, thanks!

[1/1] rtc: class: don't call cdev_device_del() when cdev_device_add() failed
commit: 789c1093f02c436b320d78a739f9610c8271cb73

Best regards,
--
Alexandre Belloni <[email protected]>