linux-kernel - Linux capabilities shouldn't be lost during setuid to non-root from root or to another non-root uid from a non-root uid.

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Message-ID: <BANLkTikTxCFHs2xb4b5QFQp3SJAEjgyRJg@mail.gmail.com>
Date:	Sun, 17 Apr 2011 23:05:59 +0900
From:	crocket <crockabiscuit@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Linux capabilities shouldn't be lost during setuid to non-root from
 root or to another non-root uid from a non-root uid.

Linux capabilities exist to split root previlege to dozens of subsets
of previleges.
But after setuid, all linux capabilities gained from a file are gone for good.
This becomes a problem with OpenVPN.

If I use --mlock option and --user option in OpenVPN, OpenVPN locks
memory with mlockall as root and drops to a non-root user specififed
by --user option.
After dropping to a non-root user, the process loses CAP_IPC_LOCK
capability gained from OpenVPN executable which I personally set.
Because the process doesn't have CAP_IPC_LOCK capability and its UID
isn't 0, further attempts to allocate memory more than "ulimit -l" to
openvpn crash OpenVPN.
This defeats the purpose of linux capabilities.
Linux capabilities exist to give a subset or subsets of previleges to
processes whose UID is greater than 0(root).

Can somebody provide or merge a patch that prevents linux from losing
capabilities after setuid?
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