linux-kernel - EUID != root + EGID = root, and CAP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <4B222C3D.2070807@icdsoft.com>
Date:	Fri, 11 Dec 2009 13:25:49 +0200
From:	Ivan Zahariev <famzah@...soft.com>
To:	linux-kernel@...r.kernel.org
CC:	Ivan Zahariev <famzah@...soft.com>
Subject: EUID != root + EGID = root, and CAP_SETGID

Hi guys,

Currently, if a process is started with EUID which is non-root, and EGID 
which IS root (for example by set-group-ID file permission + file group 
owner "root", or an account in /etc/passwd with group=0), then the 
processes is not granted CAP_SETGID.

As a result, such a process cannot change its EGID to an arbitrary one, 
even though the current EGID is the super-user "root" one. Therefore, 
such a process cannot easily drop its EGID "root" privileges to non-root 
ones, for security reasons.

This is not the case if the process starts with EUID=0. Then the 
processes is granted *both* CAP_SETUID and CAP_SETGID.

Is this an intended behavior? Shouldn't a process which is started with 
EGID=0 get CAP_SETGID too?

Thank you.

Best regads,
Ivan Zahariev

P.S. For more detailed info: 
http://blog.famzah.net/2009/12/11/linux-non-root-user-processes-which-run-with-group-root-cannot-change-their-process-group-to-an-arbitrary-one/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/