Messages in this thread | | | Date | Fri, 12 Aug 2022 21:57:31 +0530 | From | Siddh Raman Pant <> | Subject | Re: [PATCH v2] wifi: cfg80211: Fix UAF in ieee80211_scan_rx() |
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On Fri, 12 Aug 2022 20:57:58 +0530 Greg KH wrote: > rcu just delays freeing of an object, you might just be delaying the > race condition. Just moving a single object to be freed with rcu feels > very odd if you don't have another reference somewhere.
As mentioned in patch message, in net/mac80211/scan.c, we have: void ieee80211_scan_rx(struct ieee80211_local *local, struct sk_buff *skb) { ... scan_req = rcu_dereference(local->scan_req); sched_scan_req = rcu_dereference(local->sched_scan_req);
if (scan_req) scan_req_flags = scan_req->flags; ... }
So scan_req is probably supposed to be protected by RCU.
Also, in ieee80211_local's definition at net/mac80211/ieee80211_i.h, we have: struct cfg80211_scan_request __rcu *scan_req;
Thus, scan_req is indeed supposed to be protected by RCU, which this patch addresses by adding a RCU head to the type's struct, and using kfree_rcu().
The above snippet is where the UAF happens (you can refer to syzkaller's log), because __cfg80211_scan_done() is called and frees the pointer.
Thanks, Siddh
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