wifi: cfg80211: make hash table duplicates more survivable

Jiazi Li reported that they occasionally see hash table duplicates
as evidenced by the WARN_ON() in rb_insert_bss() in this code.  It
isn't clear how that happens, nor have I been able to reproduce it,
but if it does happen, the kernel crashes later, when it tries to
unhash the entry that's now not hashed.

Try to make this situation more survivable by removing the BSS from
the list(s) as well, that way it's fully leaked here (as had been
the intent in the hash insert error path), and no longer reachable
through the list(s) so it shouldn't be unhashed again later.

Link: https://lore.kernel.org/r/20231026013528.GA24122@Jiazi.LiSigned-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://msgid.link/20240607181726.36835-2-johannes@sipsolutions.netSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/scan.c

@@ -1604,7 +1604,7 @@ struct cfg80211_bss *__cfg80211_get_bss(struct wiphy *wiphy,
 }
 EXPORT_SYMBOL(__cfg80211_get_bss);
 
-static void rb_insert_bss(struct cfg80211_registered_device *rdev,
+static bool rb_insert_bss(struct cfg80211_registered_device *rdev,
 			  struct cfg80211_internal_bss *bss)
 {
 	struct rb_node **p = &rdev->bss_tree.rb_node;
@@ -1620,7 +1620,7 @@ static void rb_insert_bss(struct cfg80211_registered_device *rdev,
 
 		if (WARN_ON(!cmp)) {
 			/* will sort of leak this BSS */
-			return;
+			return false;
 		}
 
 		if (cmp < 0)
@@ -1631,6 +1631,7 @@ static void rb_insert_bss(struct cfg80211_registered_device *rdev,
 
 	rb_link_node(&bss->rbn, parent, p);
 	rb_insert_color(&bss->rbn, &rdev->bss_tree);
+	return true;
 }
 
 static struct cfg80211_internal_bss *
@@ -1657,6 +1658,34 @@ rb_find_bss(struct cfg80211_registered_device *rdev,
 	return NULL;
 }
 
+static void cfg80211_insert_bss(struct cfg80211_registered_device *rdev,
+				struct cfg80211_internal_bss *bss)
+{
+	lockdep_assert_held(&rdev->bss_lock);
+
+	if (!rb_insert_bss(rdev, bss))
+		return;
+	list_add_tail(&bss->list, &rdev->bss_list);
+	rdev->bss_entries++;
+}
+
+static void cfg80211_rehash_bss(struct cfg80211_registered_device *rdev,
+                                struct cfg80211_internal_bss *bss)
+{
+	lockdep_assert_held(&rdev->bss_lock);
+
+	rb_erase(&bss->rbn, &rdev->bss_tree);
+	if (!rb_insert_bss(rdev, bss)) {
+		list_del(&bss->list);
+		if (!list_empty(&bss->hidden_list))
+			list_del_init(&bss->hidden_list);
+		if (!list_empty(&bss->pub.nontrans_list))
+			list_del_init(&bss->pub.nontrans_list);
+		rdev->bss_entries--;
+	}
+	rdev->bss_generation++;
+}
+
 static bool cfg80211_combine_bsses(struct cfg80211_registered_device *rdev,
 				   struct cfg80211_internal_bss *new)
 {
@@ -1969,9 +1998,7 @@ __cfg80211_bss_update(struct cfg80211_registered_device *rdev,
 			bss_ref_get(rdev, bss_from_pub(tmp->pub.transmitted_bss));
 		}
 
-		list_add_tail(&new->list, &rdev->bss_list);
-		rdev->bss_entries++;
-		rb_insert_bss(rdev, new);
+		cfg80211_insert_bss(rdev, new);
 		found = new;
 	}
 
@@ -3349,19 +3376,14 @@ void cfg80211_update_assoc_bss_entry(struct wireless_dev *wdev,
 		if (!WARN_ON(!__cfg80211_unlink_bss(rdev, new)))
 			rdev->bss_generation++;
 	}
-
-	rb_erase(&cbss->rbn, &rdev->bss_tree);
-	rb_insert_bss(rdev, cbss);
-	rdev->bss_generation++;
+	cfg80211_rehash_bss(rdev, cbss);
 
 	list_for_each_entry_safe(nontrans_bss, tmp,
 				 &cbss->pub.nontrans_list,
 				 nontrans_list) {
 		bss = bss_from_pub(nontrans_bss);
 		bss->pub.channel = chan;
-		rb_erase(&bss->rbn, &rdev->bss_tree);
-		rb_insert_bss(rdev, bss);
-		rdev->bss_generation++;
+		cfg80211_rehash_bss(rdev, bss);
 	}
 
 done: