Bluetooth: Fix potential double free caused by hci_conn_unlink

The hci_conn_unlink function is being called by hci_conn_del, which
means it should not call hci_conn_del with the input parameter conn
again. If it does, conn may have already been released when
hci_conn_unlink returns, leading to potential UAF and double-free
issues.

This patch resolves the problem by modifying hci_conn_unlink to release
only conn's child links when necessary, but never release conn itself.

Reported-by: syzbot+690b90b14f14f43f4688@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-bluetooth/000000000000484a8205faafe216@google.com/
Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Reported-by: syzbot+690b90b14f14f43f4688@syzkaller.appspotmail.com
Reported-by: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Reported-by: syzbot+8bb72f86fc823817bc5d@syzkaller.appspotmail.com

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 640b951bf40a1149357357ae198c0b7b3bb0ba94..70e1655a9df6ee1e05347773792efd10dc1d489e 100644 (file)
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1083,8 +1083,18 @@ static void hci_conn_unlink(struct hci_conn *conn)
        if (!conn->parent) {
                struct hci_link *link, *t;
 
-               list_for_each_entry_safe(link, t, &conn->link_list, list)
-                       hci_conn_unlink(link->conn);
+               list_for_each_entry_safe(link, t, &conn->link_list, list) {
+                       struct hci_conn *child = link->conn;
+
+                       hci_conn_unlink(child);
+
+                       /* Due to race, SCO connection might be not established
+                        * yet at this point. Delete it now, otherwise it is
+                        * possible for it to be stuck and can't be deleted.
+                        */
+                       if (child->handle == HCI_CONN_HANDLE_UNSET)
+                               hci_conn_del(child);
+               }
 
                return;
        }
@@ -1100,13 +1110,6 @@ static void hci_conn_unlink(struct hci_conn *conn)
 
        kfree(conn->link);
        conn->link = NULL;
-
-       /* Due to race, SCO connection might be not established
-        * yet at this point. Delete it now, otherwise it is
-        * possible for it to be stuck and can't be deleted.
-        */
-       if (conn->handle == HCI_CONN_HANDLE_UNSET)
-               hci_conn_del(conn);
 }
 
 int hci_conn_del(struct hci_conn *conn)