In the Linux kernel, the following vulnerability has been resolved: net: Fix TOCTOU issue in skisreadable() sk->skprot->sockisreadable is a valid function pointer when sk resides in a sockmap. After the last skpsockput() (which usually happens when socket is removed from sockmap), sk->skprot gets restored and sk->skprot->sockisreadable becomes NULL. This makes skisreadable() racy, if the value of sk->skprot is reloaded after the initial check. Which in turn may lead to a null pointer dereference. Ensure the function pointer does not turn NULL after the check.