[v1] mac802154: Fix potential RCU dereference issue in mac802154_scan_worker

[PATCH] mac802154: Fix potential RCU dereference issue in mac802154_scan_worker

Posted by Jiawei Ye 2 months, 1 week ago

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@foxmail.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;
 	u8 page, channel;
 	int ret;
 
@@ -210,6 +211,7 @@ void mac802154_scan_worker(struct work_struct *work)
 
 	wpan_phy = scan_req->wpan_phy;
 	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,
-- 
2.34.1

Re: [PATCH] mac802154: Fix potential RCU dereference issue in mac802154_scan_worker

Posted by Przemek Kitszel 2 months, 1 week ago

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@foxmail.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,

Re: [PATCH] Fix the RCU usage in mac802154_scan_worker

Posted by Jiawei Ye 2 months, 1 week ago

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@foxmail.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?

> 
> >   	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
> 

According to the RCU usage rules, the value returned by `rcu_dereference()`
should be safely dereferenced only within the RCU read-side critical
section. It is important to note that `wpan_phy` is not obtained through
`rcu_dereference()`, so in this context, it may not be sufficient to infer
whether it is protected by RCU.

> >   	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,

Re: [PATCH] Fix the RCU usage in mac802154_scan_worker

Posted by Stefan Schmidt 2 months, 1 week ago

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@foxmail.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