netdev - Re: [PATCH] Fix the RCU usage in mac802154_scan

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Message-ID: <11239363-1608-44a4-bfab-d188f6e0934e@datenfreihafen.org>
Date: Thu, 19 Sep 2024 15:05:26 +0200
From: Stefan Schmidt <stefan@...enfreihafen.org>
To: Jiawei Ye <jiawei.ye@...mail.com>, przemyslaw.kitszel@...el.com
Cc: alex.aring@...il.com, davem@...emloft.net, david.girault@...vo.com,
 edumazet@...gle.com, kuba@...nel.org, linux-kernel@...r.kernel.org,
 linux-wpan@...r.kernel.org, miquel.raynal@...tlin.com,
 netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [PATCH] Fix the RCU usage in mac802154_scan_worker

Hello Jiawei,

On 9/19/24 14:26, Jiawei Ye wrote:
> On 9/19/24 17:01, Przemek Kitszel wrote:
>>> In the `mac802154_scan_worker` function, the `scan_req->type` field was
>>> accessed after the RCU read-side critical section was unlocked. According
>>> to RCU usage rules, this is illegal and can lead to unpredictable
>>> behavior, such as accessing memory that has been updated or causing
>>> use-after-free issues.
>>>
>>> This possible bug was identified using a static analysis tool developed
>>> by myself, specifically designed to detect RCU-related issues.
>>>
>>> To address this, the `scan_req->type` value is now stored in a local
>>> variable `scan_req_type` while still within the RCU read-side critical
>>> section. The `scan_req_type` is then used after the RCU lock is released,
>>> ensuring that the type value is safely accessed without violating RCU
>>> rules.
>>>
>>> Fixes: e2c3e6f53a7a ("mac802154: Handle active scanning")
>>> Signed-off-by: Jiawei Ye <jiawei.ye@...mail.com>
>>> ---
>>>    net/mac802154/scan.c | 4 +++-
>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/net/mac802154/scan.c b/net/mac802154/scan.c
>>> index 1c0eeaa76560..29cd84c9f69c 100644
>>> --- a/net/mac802154/scan.c
>>> +++ b/net/mac802154/scan.c
>>> @@ -180,6 +180,7 @@ void mac802154_scan_worker(struct work_struct *work)
>>>    	unsigned int scan_duration = 0;
>>>    	struct wpan_phy *wpan_phy;
>>>    	u8 scan_req_duration;
>>> +	enum nl802154_scan_types scan_req_type;
>>
>> this line violates the reverse X-mass tree rule of code formatting
> 
> Thank you for pointing out the concern regarding the violation of the
> reverse Christmas tree rule. I will adjust the placement of
> `enum nl802154_scan_types scan_req_type` to be between
> `struct cfg802154_scan_request *scan_req` and
> `struct ieee802154_sub_if_data *sdata`. If this change is suitable,
> should I resend the patch as a v2 patch?

Yes, please always increase the version whenever you change something 
and re-send. Also a ChangeLog of the changes makes it a lot easier for 
the reviewer.

regards
Stefan Schmidt