linux-kernel - Re: [PATCH] file capabilities: allow sigcont within session (v2)

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Message-ID: <47295A53.7020305@kernel.org>
Date:	Wed, 31 Oct 2007 21:47:15 -0700
From:	Andrew Morgan <morgan@...nel.org>
To:	"Serge E. Hallyn" <serue@...ibm.com>
CC:	lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Andrew Morton <akpm@...l.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Theodore Ts'o <tytso@....edu>,
	Stephen Smalley <sds@...ch.ncsc.mil>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Natalie Protasevich <protasnb@...il.com>
Subject: Re: [PATCH] file capabilities: allow sigcont within session (v2)

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[kernel/signal.c:check_kill_permission() could probably benefit from
getting more consistently indented!]

I'm not sure I can grok your comment. Did you mean:

  /* as per, check_kill_permission(), permit if tasks have same uid */

As to content:

Signed-off-by: Andrew G. Morgan <morgan@...nel.org>

Cheers

Andrew

Serge E. Hallyn wrote:
>>>From 5bff8967f45a35f858b96ca673d9bf98eac53d49 Mon Sep 17 00:00:00 2001
> From: Serge E. Hallyn <serue@...ibm.com>
> Date: Wed, 31 Oct 2007 11:22:04 -0500
> Subject: [PATCH 1/1] file capabilities: allow sigcont within session (v2)
> 
> (This is a proposed fix to http://bugzilla.kernel.org/show_bug.cgi?id=9247)
> 
> 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.
> 
> Also don't do file-capabilities signaling checks when uids for
> the processes don't match, since the standard check_kill_permission
> will have done those checks.
> 
> Signed-off-by: Serge E. Hallyn <serue@...ibm.com>
> ---
>  security/commoncap.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/security/commoncap.c b/security/commoncap.c
> index bf67871..4de6857 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -526,6 +526,15 @@ int cap_task_kill(struct task_struct *p, struct siginfo *info,
>  	if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
>  		return 0;
>  
> +	/* if tasks have same uid, then check_kill_permission did check */
> +	if (current->uid == p->uid || current->euid == p->uid ||
> +		current->uid == p->suid || current->euid == p->suid)
> +		return 0;
> +
> +	/* sigcont is permitted within same session */
> +	if (sig == SIGCONT && (task_session_nr(current)==task_session_nr(p)))
> +		return 0;
> +
>  	if (secid)
>  		/*
>  		 * Signal sent as a particular user.
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