2020-06-09 06:06:27

by Qiushi Wu

Subject: [PATCH] ipmi: code cleanup and prevent potential issue.

From: Qiushi Wu <[email protected]>

All the previous get/put operations against intf->refcount are
inside the mutex. Thus, put the last kref_put() also inside mutex
to make sure get/put functions execute in order and prevent the
potential race condition.

Signed-off-by: Qiushi Wu <[email protected]>
---
drivers/char/ipmi/ipmi_msghandler.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index e1b22fe0916c..d34343e34272 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -2583,10 +2583,11 @@ static int __bmc_get_device_id(struct ipmi_smi *intf, struct bmc_device *bmc,
*guid = bmc->guid;
}

+ kref_put(&intf->refcount, intf_free);
+
mutex_unlock(&bmc->dyn_mutex);
mutex_unlock(&intf->bmc_reg_mutex);

- kref_put(&intf->refcount, intf_free);
return rv;
}

--
2.17.1

2020-06-09 12:22:42

by Corey Minyard

Subject: Re: [PATCH] ipmi: code cleanup and prevent potential issue.

On Tue, Jun 09, 2020 at 01:04:10AM -0500, [email protected] wrote:
> From: Qiushi Wu <[email protected]>
>
> All the previous get/put operations against intf->refcount are
> inside the mutex. Thus, put the last kref_put() also inside mutex
> to make sure get/put functions execute in order and prevent the
> potential race condition.

No, this can result in a crash. intf and intf->bmc_reg_mutex will
be freed by intf_free. In fact, every call to kref_put() on intf
better be outside any mutex/lock in intf. If you saw any, that
is a bug, please report that. kref_get() is fine inside the
mutex.

Plus, this is not a race condition. get/put is atomic.

-corey

>
> Signed-off-by: Qiushi Wu <[email protected]>
> ---
> drivers/char/ipmi/ipmi_msghandler.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index e1b22fe0916c..d34343e34272 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -2583,10 +2583,11 @@ static int __bmc_get_device_id(struct ipmi_smi *intf, struct bmc_device *bmc,
> *guid = bmc->guid;
> }
>
> + kref_put(&intf->refcount, intf_free);
> +
> mutex_unlock(&bmc->dyn_mutex);
> mutex_unlock(&intf->bmc_reg_mutex);
>
> - kref_put(&intf->refcount, intf_free);
> return rv;
> }
>
> --
> 2.17.1
>