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@xxxxxxxxxxx>
> > ---
> > 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,
