From mboxrd@z Thu Jan  1 00:00:00 1970
From: Xiao Yang <yangx.jy@cn.fujitsu.com>
Date: Sat, 19 May 2018 17:04:08 +0800
Subject: [LTP] [PATCH] read_all: Drop privileges
In-Reply-To: <20180518170933.GA5094@rei>
References: <20180515095118.26282-1-rpalethorpe@suse.com>
 <20180515103042.GB7220@rei> <87bmdhyyrf.fsf@rpws.prws.suse.cz>
 <5AFBFC35.3060400@cn.fujitsu.com> <20180516114438.GA26490@rei>
 <5AFD5780.7040107@cn.fujitsu.com> <20180518170933.GA5094@rei>
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On 2018/05/19 1:09, Cyril Hrubis wrote:
> Hi!
>> Sorry, it seems a bug in open(2) instead of watchdog.
> Looks like the list of supplementary groups is at fault here.
>
> On my system I do have in /etc/group:
>
> root:x:0:root
>
> Which means that among other groups root has root suplementary group set
> when logged in.
>
> Which means that even when a program sets it's user and group ids to
> nobody the root still stays in the list of supplementary groups, which
> then is matched for files with root group ownership and hence we can
> stil open the file.
>
> Adding setgroups(0, NULL); to switch_privs() in your program "fixes" the
> behavior and we get EPERM as expected. And I guess that we should patch
> the read_all to do the same, which should fix your problem. I will apply
> the fix.
Hi Cyril,

Thanks for your detailed explanation.
I will send the fix patch as you suggested.

Thanks,
Xiao Yang