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From:   Jann Horn <jannh@google.com>
Date:   Thu, 25 Oct 2018 15:45:29 +0200
Message-ID: <CAG48ez2aJD1wcz3UjhaQvgqhg5UMeQ_-iMZesA=SfhYwUdGGyA@mail.gmail.com>
Subject: Re: [PATCH v2] kernel/signal: Signal-based pre-coredump notification
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     enkechen@cisco.com, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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On Wed, Oct 24, 2018 at 3:30 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
> Enke Chen <enkechen@cisco.com> writes:
> > For simplicity and consistency, this patch provides an implementation
> > for signal-based fault notification prior to the coredump of a child
> > process. A new prctl command, PR_SET_PREDUMP_SIG, is defined that can
> > be used by an application to express its interest and to specify the
> > signal (SIGCHLD or SIGUSR1 or SIGUSR2) for such a notification. A new
> > signal code (si_code), CLD_PREDUMP, is also defined for SIGCHLD.
> >
> > Changes to prctl(2):
> >
> >    PR_SET_PREDUMP_SIG (since Linux 4.20.x)
> >           Set the child pre-coredump signal of the calling process to
> >           arg2 (either SIGUSR1, or SIUSR2, or SIGCHLD, or 0 to clear).
> >           This is the signal that the calling process will get prior to
> >           the coredump of a child process. This value is cleared across
> >           execve(2), or for the child of a fork(2).
> >
> >           When SIGCHLD is specified, the signal code will be set to
> >           CLD_PREDUMP in such an SIGCHLD signal.
[...]
> Ugh.  Your test case is even using signalfd.  So you don't even want
> this signal to be delivered as a signal.

Just to make sure everyone's on the same page: You're suggesting that
it might make sense to deliver the pre-dump notification via a new
type of file instead (along the lines of signalfd, timerfd, eventfd
and so on)?