[PATCH] Bluetooth: Fix UAF in hci_conn_hash_flush again

[Ruihan Li <lrh2000@pku.edu.cn>]

Commit 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple
hcon") reintroduces a previously fixed bug [1] ("KASAN: slab-use-after-free
Read in hci_conn_hash_flush"). This bug was originally fixed by commit
5dc7d23e167e ("Bluetooth: hci_conn: Fix possible UAF").

The hci_conn_unlink function was added to avoid invalidating the link
traversal caused by successive hci_conn_del operations releasing extra
connections. However, currently hci_conn_unlink itself also releases extra
connections, resulted in the reintroduced bug.

This patch follows a more robust solution for cleaning up all connections,
by repeatedly removing the first connection until there are none left. This
approach does not rely on the inner workings of hci_conn_del and ensures
proper cleanup of all connections.

However, we need to make sure that hci_conn_del never fails. Indeed it
doesn't, as it now always returns zero. To make this a bit clearer, this
patch also changes its return type to void.

Reported-by: syzbot+8bb72f86fc823817bc5d@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8bb72f86fc823817bc5d
Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
---
 include/net/bluetooth/hci_core.h |  2 +-
 net/bluetooth/hci_conn.c         | 28 ++++++++++++----------------
 2 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index a6c8aee2f..8baf34639 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -1327,7 +1327,7 @@ int hci_le_create_cis(struct hci_conn *conn);
 
 struct hci_conn *hci_conn_add(struct hci_dev *hdev, int type, bdaddr_t *dst,
 			      u8 role);
-int hci_conn_del(struct hci_conn *conn);
+void hci_conn_del(struct hci_conn *conn);
 void hci_conn_hash_flush(struct hci_dev *hdev);
 void hci_conn_check_pending(struct hci_dev *hdev);
 
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 640b951bf..85c34c837 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1109,7 +1109,7 @@ static void hci_conn_unlink(struct hci_conn *conn)
 		hci_conn_del(conn);
 }
 
-int hci_conn_del(struct hci_conn *conn)
+void hci_conn_del(struct hci_conn *conn)
 {
 	struct hci_dev *hdev = conn->hdev;
 
@@ -1160,8 +1160,6 @@ int hci_conn_del(struct hci_conn *conn)
 	 * rest of hci_conn_del.
 	 */
 	hci_conn_cleanup(conn);
-
-	return 0;
 }
 
 struct hci_dev *hci_get_route(bdaddr_t *dst, bdaddr_t *src, uint8_t src_type)
@@ -2462,22 +2460,20 @@ void hci_conn_enter_active_mode(struct hci_conn *conn, __u8 force_active)
 /* Drop all connection on the device */
 void hci_conn_hash_flush(struct hci_dev *hdev)
 {
-	struct hci_conn_hash *h = &hdev->conn_hash;
-	struct hci_conn *c, *n;
+	struct list_head *head = &hdev->conn_hash.list;
+	struct hci_conn *conn;
 
 	BT_DBG("hdev %s", hdev->name);
 
-	list_for_each_entry_safe(c, n, &h->list, list) {
-		c->state = BT_CLOSED;
-
-		hci_disconn_cfm(c, HCI_ERROR_LOCAL_HOST_TERM);
-
-		/* Unlink before deleting otherwise it is possible that
-		 * hci_conn_del removes the link which may cause the list to
-		 * contain items already freed.
-		 */
-		hci_conn_unlink(c);
-		hci_conn_del(c);
+	/* We should not traverse the list here, because hci_conn_del
+	 * can remove extra links, which may cause the link traversal
+	 * to hit items that have already been released.
+	 */
+	while ((conn = list_first_entry_or_null(head,
+				struct hci_conn, list)) != NULL) {
+		conn->state = BT_CLOSED;
+		hci_disconn_cfm(conn, HCI_ERROR_LOCAL_HOST_TERM);
+		hci_conn_del(conn);
 	}
 }
 
-- 
2.40.0