linux-kernel - Re: [PATCH v2] kernel/signal: Signal-based pre-coredump notification

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Date:   Thu, 25 Oct 2018 15:45:29 +0200
From:   Jann Horn <jannh@...gle.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     enkechen@...co.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Kate Stewart <kstewart@...uxfoundation.org>, deller@....de,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        christian@...uner.io, Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, Dave.Martin@....com,
        mchehab+samsung@...nel.org, Michal Hocko <mhocko@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        guro@...com, Marcos Souza <marcos.souza.org@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, linux@...inikbrodowski.net,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        yang.shi@...ux.alibaba.com, Kees Cook <keescook@...omium.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Victor Kamensky <kamensky@...co.com>,
        xe-linux-external@...co.com, sstrogin@...co.com
Subject: Re: [PATCH v2] kernel/signal: Signal-based pre-coredump notification

On Wed, Oct 24, 2018 at 3:30 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Enke Chen <enkechen@...co.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)?