linux-kernel - Re: [PATCH 2/9] signal/seccomp: Refactor seccomp signal and coredump generation

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Message-ID: <87im1xx0az.fsf@disp2133>
Date:   Mon, 28 Jun 2021 14:21:24 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kees Cook <keescook@...omium.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Michael Schmitz <schmitzmic@...il.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Oleg Nesterov <oleg@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        alpha <linux-alpha@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 2/9] signal/seccomp: Refactor seccomp signal and coredump generation

Kees Cook <keescook@...omium.org> writes:

> On Thu, Jun 24, 2021 at 01:59:55PM -0500, Eric W. Biederman wrote:
>> 
>> Factor out force_sig_seccomp from the seccomp signal generation and
>> place it in kernel/signal.c.  The function force_sig_seccomp takes a
>> paramter force_coredump to indicate that the sigaction field should be
>> reset to SIGDFL so that a coredump will be generated when the signal
>> is delivered.
>
> Ah! This is the part I missed when I was originally trying to figure
> out the coredump stuff. It's the need for setting a default handler
> (i.e. doing a coredump)?

Yes.  If we don't force the handler to SIG_DFL someone might catch
SIGSYS.

>> force_sig_seccomp is then used to replace both seccomp_send_sigsys
>> and seccomp_init_siginfo.
>> 
>> force_sig_info_to_task gains an extra parameter to force using
>> the default signal action.
>> 
>> With this change seccomp is no longer a special case and there
>> becomes exactly one place do_coredump is called from.
>
> Looks good to me. This may benefit from force_sig_seccomp() to be wrapped
> in an #ifdef CONFIG_SECCOMP.

At which point Linus will probably be grumpy with me for introducing
#ifdefs.

I suspect seccomp at this point is sufficiently common that is probably
more productive to figure out how to remove #ifdef  CONFIG_SECCOMP.

> (This patch reminds me that the seccomp self tests don't check for core
> dumps...)

This patch is slightly wrong in that it kept the call to do_group_exit
when it can never be reached.

Eric