ptrace: fix ptrace vs tasklist_lock race

As explained by Alexander Fyodorov <halcy@yandex.ru>:

|read_lock(&tasklist_lock) in ptrace_stop() is converted to mutex on RT kernel,
|and it can remove __TASK_TRACED from task->state (by moving  it to
|task->saved_state). If parent does wait() on child followed by a sys_ptrace
|call, the following race can happen:
|
|- child sets __TASK_TRACED in ptrace_stop()
|- parent does wait() which eventually calls wait_task_stopped() and returns
|  child's pid
|- child blocks on read_lock(&tasklist_lock) in ptrace_stop() and moves
|  __TASK_TRACED flag to saved_state
|- parent calls sys_ptrace, which calls ptrace_check_attach() and wait_task_inactive()

The patch is based on his initial patch where an additional check is
added in case the __TASK_TRACED moved to ->saved_state. The pi_lock is
taken in case the caller is interrupted between looking into ->state and
->saved_state.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

0 files changed, 0 insertions, 0 deletions