linux-kernel - chown: s-Bits: to clear or not to clear

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Date:	Tue, 16 Jul 2013 10:29:01 +0200
From:	"Ulrich Windl" <Ulrich.Windl@...uni-regensburg.de>
To:	<linux-kernel@...r.kernel.org>
Cc:	"Ulrich Windl" <Ulrich.Windl@...uni-regensburg.de>
Subject: chown: s-Bits: to clear or not to clear

Hi folks,

I discovered (SLES11 SP2 with kernel  3.0.80) that a chown executed by root (from non-root to non-root user) clears any s-Bits that were set for the old owner.

The man page (man 2 chown) says:
       When  the  owner  or  group of an executable file are changed by a non-
       superuser, the S_ISUID and S_ISGID mode bits are cleared.   POSIX  does
       not specify whether this also should happen when root does the chown();
       the Linux behavior depends on the kernel version.  In case  of  a  non-
       group-executable  file (i.e., one for which the S_IXGRP bit is not set)
       the S_ISGID bit indicates mandatory locking, and is not  cleared  by  a
       chown().

As there are good arguments for and against clearing the s-Bits during chown, there are probably only good arguments for having an option for chown(1) to preserve the s-Bits. What do you think? (I know this is the wrong list for discussing utils).

Regards,
Ulrich Windl


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