nl80211_pmsr_start() assigns the request cookie, calls the driver's
->start_pmsr() callback, and only then adds the request to
wdev->pmsr_list, without holding pmsr_lock for the addition.

mac80211_hwsim saves the request in its start callback and returns. Since
nl80211 uses parallel_ops, an immediate REPORT_PMSR can then run before
nl80211_pmsr_start() reaches its post-start list_add_tail(). hwsim also
dispatches reports from its virtio receive workqueue. Completion removes
the request from wdev->pmsr_list under pmsr_lock and frees it.

Thus completion can precede publication, race the unlocked list mutation,
or free the request before nl80211_pmsr_start() reads req->cookie for the
netlink reply.

Add the request to wdev->pmsr_list under pmsr_lock before calling the
driver, and use a cookie value saved before the call so the request is not
dereferenced after a successful start. On an error return the driver has
not retained or completed the request, so remove it from the list under the
lock and free it.

Fixes: 9bb7e0f24e7e ("cfg80211: add peer measurement with FTM initiator API")
Link: https://lore.kernel.org/all/20260723010916.76433-1-enderaoelyther@gmail.com/
Assisted-by: Codex:gpt-5
Assisted-by: Claude:opus-4.8
Signed-off-by: Zhao Li <enderaoelyther@gmail.com>
---
Changes in v2:
- Drop callback documentation that implied synchronous completion was
  supported.
- Reword the local comment as defensive handling for races or broken
  drivers that complete the request before ->start_pmsr() returns.
---
 net/wireless/pmsr.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/net/wireless/pmsr.c b/net/wireless/pmsr.c
index d1e2fae5bc0e..97449bcb9a22 100644
--- a/net/wireless/pmsr.c
+++ b/net/wireless/pmsr.c
@@ -420,6 +420,7 @@ int nl80211_pmsr_start(struct sk_buff *skb, struct genl_info *info)
 	const struct cfg80211_pmsr_capabilities *capa;
 	struct cfg80211_pmsr_request *req;
 	struct nlattr *peers, *peer;
+	u64 cookie;
 
 	capa = rdev->wiphy.pmsr_capa;
 
@@ -521,14 +522,27 @@ int nl80211_pmsr_start(struct sk_buff *skb, struct genl_info *info)
 	}
 	req->cookie = cfg80211_assign_cookie(rdev);
 	req->nl_portid = info->snd_portid;
+	cookie = req->cookie;
+
+	/*
+	 * Add to the list before the driver call; under races or broken
+	 * drivers, completion may free the request before rdev_start_pmsr()
+	 * returns. Use the saved cookie below.
+	 */
+	spin_lock_bh(&wdev->pmsr_lock);
+	list_add_tail(&req->list, &wdev->pmsr_list);
+	spin_unlock_bh(&wdev->pmsr_lock);
 
 	err = rdev_start_pmsr(rdev, wdev, req);
-	if (err)
+	if (err) {
+		/* An error return leaves the request owned by this path. */
+		spin_lock_bh(&wdev->pmsr_lock);
+		list_del(&req->list);
+		spin_unlock_bh(&wdev->pmsr_lock);
 		goto out_err;
+	}
 
-	list_add_tail(&req->list, &wdev->pmsr_list);
-
-	nl_set_extack_cookie_u64(info->extack, req->cookie);
+	nl_set_extack_cookie_u64(info->extack, cookie);
 	return 0;
 out_err:
 	kfree(req);
-- 
2.50.1 (Apple Git-155)