linux-kernel - Re: [PATCH 03/26] signal: Do not perform permission checks when sending pdeath

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Date:   Tue, 6 Jun 2017 23:42:08 +0200
From:   Richard Weinberger <richard.weinberger@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "open list:ABI/API" <linux-api@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Roland McGrath <roland@...k.frob.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 03/26] signal: Do not perform permission checks when
 sending pdeath_signal

Eric,

On Tue, Jun 6, 2017 at 9:03 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> This fixes and old old regression.  When Roland switched from
> sending pdeath_signal with send_sig() to send_group_sig_info
> it gained a permission check, and started taking the tasklist
> lock.  Roland earlier fixed the double taking of the tasklist
> lock in 3f2a0d1df938 ("[PATCH] fix pdeath_signal SMP locking")
> but pdeath_signal still performs an unnecessary permission
> check.
>
> Ordinarily I would be hesitant at fixing an ancient regression but
> a permission check for our parent sending to us is almost never
> likely to fail (so it is unlikely anyone has noticed), and it
> is stupid.  It makes absolutely no sense to see if our
> parent has permission to send us a signal we requested be
> sent to us.

Another side effect of this change is that audit_signal_info() is no longer
being called. AFAICT this is a user space visible change.

-- 
Thanks,
//richard