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From: Oleg Nesterov <oleg@redhat.com>
To: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Tejun Heo <tj@kernel.org>,
	jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org, akpm@linux-foundation.org,
	indan@nul.nu
Subject: Re: Ptrace documentation, draft #1
Date: Mon, 23 May 2011 14:10:11 +0200	[thread overview]
Message-ID: <20110523121011.GA5799@redhat.com> (raw)
In-Reply-To: <BANLkTi=bRb+NCqqS9+ptzxHVOjKKXhZgsg@mail.gmail.com>

On 05/20, Denys Vlasenko wrote:
>
> On Thu, May 19, 2011 at 9:49 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> > Once again, PTRACE_KILL == ptrace(PTRACE_CONT, SIGKILL), except it
> > doesn't return the error if the tracee is not stopped.
>
> Oleg, this doesn't explain the resulting behavior in terms understandable
> to mere mortals. *What will happen* when user does ptrace(PTRACE_KILL)?
>
> Yes, it's obvious that the tracee gets SIGKILLed,

No, it is not necessarily killed. Once again, it is equivalent to PTRACE_CONT
except it returns 0 (but does nothing) if the tracee is not stopped.

"does nothing" is not 100% true, it does wake_up_process() but this shouldn't
be documented, this should be fixed.

> >> >> ??? can this SIGTRAP be distinguished from "real" user-generated SIGTRAP
> >> >>     by looking at its siginfo?
> >> >
> >> > Afaics no. Well, except .si_pid shows that the signal was sent by the
> >> > tracing process to itself.
> >>
> >> What about si_code? Is it set to SI_KERNEL for this signal?
> >
> > No, SI_USER.
>
> This is stupid. This signal is sent by kernel. Why is it flagged as "from user"?
> Maybe we should change it?

Well, may be... I dunno actually. Hmm. On a second thought you are probably
right. ptrace_report_syscall() does send_sig() too, but it sets SI_KERNEL.
I am starting to think, at least they should use the same si_code.

> (BTW, where is it generated in the kernel source? I found
> PTRACE_EVENT_EXEC generation, but failed to find
> "old-school SIGTRAP" generation code...)

tracehook_report_exec()->send_sig(SIGTRAP).

Oleg.


  reply	other threads:[~2011-05-23 12:11 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-15 20:35 Ptrace documentation, draft #1 Denys Vlasenko
2011-05-16  9:15 ` Tejun Heo
2011-05-16 15:31 ` Oleg Nesterov
2011-05-16 15:52   ` Tejun Heo
2011-05-16 16:53     ` Oleg Nesterov
2011-05-16 17:20       ` Tejun Heo
2011-05-16 17:48         ` Oleg Nesterov
2011-05-18 15:02       ` Denys Vlasenko
2011-05-18 15:02   ` Denys Vlasenko
2011-05-19 19:49     ` Oleg Nesterov
2011-05-20 18:02       ` Denys Vlasenko
2011-05-23 12:10         ` Oleg Nesterov [this message]
2011-05-23 14:10           ` ptrace_resume->wake_up_process (Was: Ptrace documentation, draft #1) Oleg Nesterov
2011-05-23 16:17             ` Linus Torvalds
2011-05-23 17:23               ` Oleg Nesterov
2011-05-25 20:08                 ` [GIT PULL] PTRACE_KILL/wakeup fix for v2.6.40 Oleg Nesterov
2011-05-23 17:05             ` [PATCH 0/2] Was: ptrace_resume->wake_up_process Oleg Nesterov
2011-05-23 17:05               ` [PATCH 1/2] ptrace: ptrace_resume() shouldn't wake up !TASK_TRACED thread Oleg Nesterov
2011-05-23 17:05               ` [PATCH 2/2] signal: sys_pause() should check signal_pending() Oleg Nesterov

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