Re: [PATCHv2] ptrace: fix PTRACE_LISTEN race corrupting task->state

[Andrew Morton]

On Tue, 04 Apr 2017 14:47:34 -0700 bsegall@xxxxxxxxxx wrote:

> In PT_SEIZED + LISTEN mode STOP/CONT 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. This causes
> it to instead clobber TASK_WAKING, allowing a subsequent wakeup against
> TRACED while the task is still on the rq wake_list, corrupting it.

The changelog doesn't convey the urgency of the fix.  To understand
this we'll need to know the user-visible impact of the bug and the
likelihood of someone hitting it.

Also your suggestion regarding which kernel version(s) should be fixed
(and the reasoning) is always valuable.