linux-kernel - Re: Posix file capabilities in 2.6.24rc2

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Date:	Wed, 14 Nov 2007 12:02:35 -0600
From:	"Serge E. Hallyn" <sergeh@...ibm.com>
To:	Chris Friedhoff <chris@...edhoff.org>
Cc:	Serge E Hallyn <sergeh@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Posix file capabilities in 2.6.24rc2

Quoting Chris Friedhoff (chris@...edhoff.org):
> Hello Serge,
> 
> I wanted only to express what I observed.
> 
> A "yes it should" confirms its ok.
> 
> And yes, I haven't looked into the patches and the name and commentary
> of file-capabilities-clear-fcaps-on-inode-change.patch explains this
> already.
> I'm preparing to update my page http://www.friedhoff.org/fscaps.html
> for 2.6.24, and I also want to explain what one has to take into account
> or be beware off. If I stumble about this, I think others will also
> (imho).
> 
> I have written a script to change suid binaries and servers,
> automating the examples I give on the webpage.

Cool, sounds very useful.

> In the sequence of commands I was setting fscaps and than chown the
> binary. Now with the aforementioned patch the fscaps are removed when
> I chown and the script wasn't working anymore. My point is not my
> script, it's being surprised and being a bit at a loss. Documenting
> this helps to clarify things and users to adopt this feature.
> 
> 
> The matter with "xinit:  Operation not permitted..." happens, when I
> (unprivileged user) close a from a console started X session. Similar to
> Andrew Morton'S http://lkml.org/lkml/2006/11/23/15 . The 2.6.24-rc2
> kernel has capabilties enabled but /usr/bin/xinit has no capabilities
> set. It remains the black screen with a cursor, the windowmanager is
> closed. Is this known? Is this a problem? Does anyone else observes
> this?

I'm setting up a vm to play with this.  Will look into it.

Oh, looking at a few branches, I see that the patch for bug# 9247
(on bugzilla.kernel.org) isn't in 2.6.24-rc2 yet.  Can you check
whether the following patch fixes it?

thanks,
-serge

>From 347faf5852644b91632813885784104f4cdb640a Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue@...ibm.com>
Date: Wed, 14 Nov 2007 13:00:52 -0500
Subject: [PATCH 1/1] file capabilities: allow sigcont within session (v2.6.24-rc2)

Allow sigcont to be sent to a process with greater capabilities
if it is in the same session.  Otherwise, a shell from which
I've started a root shell and done 'suspend' can't be restarted
by the parent shell.

(this patch against v2.6.24-rc2)

Signed-off-by: Serge E. Hallyn <serue@...ibm.com>
---
 security/commoncap.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/security/commoncap.c b/security/commoncap.c
index bf67871..c9f6867 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -534,6 +534,8 @@ int cap_task_kill(struct task_struct *p, struct siginfo *info,
 		 * Used only by usb drivers?
 		 */
 		return 0;
+	if (sig == SIGCONT && (task_session_nr(current)==task_session_nr(p)))
+		return 0;
 	if (cap_issubset(p->cap_permitted, current->cap_permitted))
 		return 0;
 	if (capable(CAP_KILL))
-- 
1.5.1.1.GIT

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