linux-kernel - Re: [PATCH] mac802154: Fix potential RCU dereference issue in mac802154_scan

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Message-ID: <f3c26426-7ebb-4b8b-9443-f604292a53a9@intel.com>
Date: Thu, 19 Sep 2024 11:01:07 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Jiawei Ye <jiawei.ye@...mail.com>, <miquel.raynal@...tlin.com>
CC: <linux-wpan@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <alex.aring@...il.com>,
	<stefan@...enfreihafen.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <david.girault@...vo.com>
Subject: Re: [PATCH] mac802154: Fix potential RCU dereference issue in
 mac802154_scan_worker

On 9/19/24 09:16, Jiawei Ye 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

>   	u8 page, channel;
>   	int ret;
>   
> @@ -210,6 +211,7 @@ void mac802154_scan_worker(struct work_struct *work)
>   
>   	wpan_phy = scan_req->wpan_phy;

this line (not yours) just saves the first level of pointer, but then
accesses wpan_phy->... outside of the rcu_read_lock() section, for me
it's very similar case to what you are fixing here

>   	scan_req_duration = scan_req->duration;
> +	scan_req_type = scan_req->type;
>   
>   	/* Look for the next valid chan */
>   	page = local->scan_page;
> @@ -246,7 +248,7 @@ void mac802154_scan_worker(struct work_struct *work)
>   		goto end_scan;
>   	}
>   
> -	if (scan_req->type == NL802154_SCAN_ACTIVE) {
> +	if (scan_req_type == NL802154_SCAN_ACTIVE) {
>   		ret = mac802154_transmit_beacon_req(local, sdata);
>   		if (ret)
>   			dev_err(&sdata->dev->dev,