cfg80211: avoid double free of PMSR request

If cfg80211_pmsr_process_abort() moves all the PMSR requests that
need to be freed into a local list before aborting and freeing them.
As a result, it is possible that cfg80211_pmsr_complete() will run in
parallel and free the same PMSR request.

Fix it by freeing the request in cfg80211_pmsr_complete() only if it
is still in the original pmsr list.

Cc: stable@vger.kernel.org
Fixes: 9bb7e0f2 ("cfg80211: add peer measurement with FTM initiator API")
Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210618133832.1fbef57e269a.I00294bebdb0680b892f8d1d5c871fd9dbe785a5e@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/pmsr.c

@@ -334,6 +334,7 @@ void cfg80211_pmsr_complete(struct wireless_dev *wdev,
 			    gfp_t gfp)
 {
 	struct cfg80211_registered_device *rdev = wiphy_to_rdev(wdev->wiphy);
+	struct cfg80211_pmsr_request *tmp, *prev, *to_free = NULL;
 	struct sk_buff *msg;
 	void *hdr;
 
@@ -364,9 +365,20 @@ void cfg80211_pmsr_complete(struct wireless_dev *wdev,
 	nlmsg_free(msg);
 free_request:
 	spin_lock_bh(&wdev->pmsr_lock);
-	list_del(&req->list);
+	/*
+	 * cfg80211_pmsr_process_abort() may have already moved this request
+	 * to the free list, and will free it later. In this case, don't free
+	 * it here.
+	 */
+	list_for_each_entry_safe(tmp, prev, &wdev->pmsr_list, list) {
+		if (tmp == req) {
+			list_del(&req->list);
+			to_free = req;
+			break;
+		}
+	}
 	spin_unlock_bh(&wdev->pmsr_lock);
-	kfree(req);
+	kfree(to_free);
 }
 EXPORT_SYMBOL_GPL(cfg80211_pmsr_complete);