"Eric W. Biederman" <ebied...@xmission.com> writes:
> "Eric W. Biederman" <ebied...@xmission.com> writes:
>
>> Asking wait_task_inactive to verify that tsk->__state == __TASK_TRACED
>> was needed to detect the when ptrace_stop would decide not to stop
>> after calling "set_special_state(TASK_TRACED)". With the recent
>> cleanups ptrace_stop will always stop after calling set_special_state.
>>
>> Take advatnage of this by no longer asking wait_task_inactive to
>> verify the state. If a bug is hit and wait_task_inactive does not
>> succeed warn and return -ESRCH.
>
> As Oleg noticed upthread there are more reasons than simply
> !current->ptrace for wait_task_inactive to fail. In particular a fatal
> signal can be received any time before JOBCTL_DELAY_SIGKILL.
>
> So this change is not safe. I will respin this one.
Bah. I definitely need to update the description so there is going to
be a v2.
I confused myself. This change is safe because ptrace_freeze_traced
fails if there is a pending fatal signal, and arranges that no new fatal
signals will wake up the task.
Eric
>> Signed-off-by: "Eric W. Biederman" <ebied...@xmission.com>
>> ---
>> kernel/ptrace.c | 14 +++-----------
>> 1 file changed, 3 insertions(+), 11 deletions(-)
>>
>> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
>> index 16d1a84a2cae..0634da7ac685 100644
>> --- a/kernel/ptrace.c
>> +++ b/kernel/ptrace.c
>> @@ -265,17 +265,9 @@ static int ptrace_check_attach(struct task_struct
>> *child, bool ignore_state)
>> }
>> read_unlock(&tasklist_lock);
>>
>> - if (!ret && !ignore_state) {
>> - if (!wait_task_inactive(child, __TASK_TRACED)) {
>> - /*
>> - * This can only happen if may_ptrace_stop() fails and
>> - * ptrace_stop() changes ->state back to TASK_RUNNING,
>> - * so we should not worry about leaking __TASK_TRACED.
>> - */
>> - WARN_ON(READ_ONCE(child->__state) == __TASK_TRACED);
>> - ret = -ESRCH;
>> - }
>> - }
>> + if (!ret && !ignore_state &&
>> + WARN_ON_ONCE(!wait_task_inactive(child, 0)))
>> + ret = -ESRCH;
>>
>> return ret;
>> }
>
> Eric
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