linux-kernel - Re: [RFC 4/5] user namespaces: allow killing tasks in your own or child userns

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Date:	Fri, 17 Dec 2010 11:31:40 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	LSM <linux-security-module@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	Kees Cook <kees.cook@...onical.com>,
	containers@...ts.linux-foundation.org,
	kernel list <linux-kernel@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Michael Kerrisk <michael.kerrisk@...il.com>
Subject: Re: [RFC 4/5] user namespaces: allow killing tasks in your own or child userns

"Serge E. Hallyn" <serge@...lyn.com> writes:

> Changelog:
> 	Dec 8: Fixed bug in my check_kill_permission pointed out by
> 	       Eric Biederman.
> 	Dec 13: Apply Eric's suggestion to pass target task into kill_ok_by_cred()
> 	        for clarity
>
> Signed-off-by: Serge E. Hallyn <serge.hallyn@...onical.com>
> ---
>  kernel/signal.c |   33 ++++++++++++++++++++++++++++-----
>  1 files changed, 28 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 4e3cff1..499bd36 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -659,11 +686,7 @@ static int check_kill_permission(int sig, struct siginfo *info,
>  	cred = current_cred();
>  	tcred = __task_cred(t);
Nit pick  you don't need to compute cred and tcred here now.

>  	if (!same_thread_group(current, t) &&
> -	    (cred->euid ^ tcred->suid) &&
> -	    (cred->euid ^ tcred->uid) &&
> -	    (cred->uid  ^ tcred->suid) &&
> -	    (cred->uid  ^ tcred->uid) &&
> -	    !capable(CAP_KILL)) {
> +	    !kill_ok_by_cred(t)) {
>  		switch (sig) {
>  		case SIGCONT:
>  			sid = task_session(t);
--
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