Re: [PATCH] ptrace: fix PTRACE_LISTEN race corrupting task->state

From: bsegall
Date: Wed Feb 22 2017 - 12:56:53 EST

Oleg Nesterov <oleg@xxxxxxxxxx> writes:

> On 02/21, bsegall@xxxxxxxxxx wrote:
>> In PT_SEIZED + LISTEN mode SIGSTOP/SIGCONT signals cause a wakeup
>> against __TASK_TRACED. If this races with the ptrace_unfreeze_traced at
>> the end of a PTRACE_LISTEN, this can wake the task /after/ the check
>> against __TASK_TRACED, but before the reset of state to TASK_TRACED.
> Oh, thanks...
> note also that PTRACE_LISTEN itself can do ptrace_signal_wake_up(true),
>> This causes it to instead clobber TASK_WAKING,
> even if it is already TASK_RUNNING it is simply wrong to set TASK_TRACED
> in both cases, right?

Yeah, that's also wrong and could possibly lead to different errors, but
is likely to work out by accident when say ttwu checks on_rq and sees true.

> Thanks. The patch looks good at first glance, but let me think a bit...
> perhaps we should change PTRACE_LISTEN instead, not sure.
> Oleg.