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Date:      Mon, 27 Feb 2012 11:29:51 +0200
From:      Konstantin Belousov <kostikbel@gmail.com>
To:        Mikolaj Golub <trociny@freebsd.org>
Cc:        svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org>
Subject:   Re: svn commit: r232181 - in head/sys: kern sys
Message-ID:  <20120227092951.GB55074@deviant.kiev.zoral.com.ua>
In-Reply-To: <864nucd5jc.fsf@in138.ua3>
References:  <201202261425.q1QEPm9g069102@svn.freebsd.org> <20120227082811.GC1363@garage.freebsd.pl> <864nucd5jc.fsf@in138.ua3>

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On Mon, Feb 27, 2012 at 10:49:59AM +0200, Mikolaj Golub wrote:
>=20
> On Mon, 27 Feb 2012 09:28:11 +0100 Pawel Jakub Dawidek wrote:
>=20
>  PJD> On Sun, Feb 26, 2012 at 02:25:48PM +0000, Mikolaj Golub wrote:
>  >> Author: trociny
>  >> Date: Sun Feb 26 14:25:48 2012
>  >> New Revision: 232181
>  >> URL: http://svn.freebsd.org/changeset/base/232181
>  >>=20
>  >> Log:
>  >>   Add sysctl to retrieve or set umask of another process.
>=20
>  PJD> "set umask of another process"? This seems... weird. What's the pur=
pose
>  PJD> of this change?
>=20
> When we were discussing this with Kostik and Robert, and I asked if it co=
uld
> be useful to have the sysctl rw, Kostik described a real situation when h=
e had
> had to change umask of another process: umask had not been set properly o=
n an
> aplication start but it could not be restarted until the end of the day.
> Kostik was able to fix it using gdb but having an easier way looked usefu=
l.
kgdb, not gdb.

It is indeed possible to write a ptrace-based utility that inject a code
payload that would change umask. Since this is very risky but indeed possib=
le,
having the straighforward kernel facility is justified.

Patch puts the same restrictions on the caller as ptrace().

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