Re: [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP support to PTRACE_GET_SYSCALL_INFO

[Oleg Nesterov <oleg@redhat.com>]

On 11/28, Dmitry V. Levin wrote:
>
> > Just like ptrace_request(PTRACE_LISTEN)
> > does but you can do this lockless (no need to lock_task_sighand()).
>
> Why this can be done lockless?  All other places in that file do
> the locking,

PTRACE_LISTEN too doesn't need lock_task_sighand() to access ->last_siginfo,
this code predates ptrace_freeze_traced() which ensures that the tracee can't
go away and clear ->last_siginfo.

However, unlike ptrace_get_syscall(), PTRACE_LISTEN needs spin_lock_irq(siglock),
it modifies ->jobctl and calls signal_wake_up().

> > Of course, debugger can do PTRACE_SETSIGINFO and confuse itself but probably we
> > do not care?
>
> The only potential issue I could think of is whether PTRACE_SETSIGINFO
> could be used this way to cause an information leak by making
> PTRACE_GET_SYSCALL_INFO access some unrelated data.

Well, afaics ptrace_get_syscall() does nothing "special", debugger can use other
PTRACE_ requests to get the same info?

Oleg.