On 3/6/20 6:17 AM, Eric W. Biederman wrote: > Bernd Edlinger <bernd.edlinger@xxxxxxxxxx> writes: > >> On 3/5/20 10:16 PM, Eric W. Biederman wrote: >>> >>> The cred_guard_mutex is problematic. The cred_guard_mutex is held >>> over the userspace accesses as the arguments from userspace are read. >>> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other >>> threads are killed. The cred_guard_mutex is held over >>> "put_user(0, tsk->clear_child_tid)" in exit_mm(). >>> I am all for this patch, and the direction it is heading, Eric. I just wanted to add a note that I think it is possible that exec_mm_release can also invoke put_user(0, tsk->clear_child_tid), under the new exec_update_mutex, since vm_access increments the mm->mm_users, under the cred_update_mutex, but releases the mutex, and the caller can hold the reference for a while and then exec_mmap is not releasing the last reference. Bernd.
