linux-kernel - Re: [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP support to PTRACE_GET_SYSCALL

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Message-ID: <20181128123545.GA30395@redhat.com>
Date:   Wed, 28 Nov 2018 13:35:46 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     Elvira Khabirova <lineprinter@...linux.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Eugene Syromyatnikov <esyr@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        strace-devel@...ts.strace.io, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP
 support to PTRACE_GET_SYSCALL_INFO

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.