linux-kernel - Re: [PATCH] pidns: limit the nesting depth of pid namespaces

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

Message-ID: <20121020152100.GA28039@redhat.com>
Date:	Sat, 20 Oct 2012 17:21:00 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Vagin <avagin@...nvz.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] pidns: limit the nesting depth of pid namespaces

On 10/12, Andrew Vagin wrote:
>
> 'struct pid' is a "variable sized struct" - a header with an array
> of upids at the end.
>
> A size of the array depends on a level (depth) of pid namespaces. Now
> a level of pidns is not limited, so 'struct pid' can be more than one
> page.
>
> Looks reasonable, that it should be less than a page. MAX_PIS_NS_LEVEL
> is not calculated from PAGE_SIZE, because in this case it depends on
> architectures, config options and it will be reduced, if someone adds a
> new fields in struct pid or struct upid.
>
> I suggest to set MAX_PIS_NS_LEVEL = 32, because it saves ability to
> expand "struct pid" and it's more than enough for all known for me
> use-cases.  When someone finds a reasonable use case, we can add a
> config option or a sysctl parameter.
>
> In addition it will reduce effect of another problem, when we have many
> nested namespaces and the oldest one starts dying.  zap_pid_ns_processe
> will be called for each namespace and find_vpid will be called for each
> process in a namespace. find_vpid will be called minimum max_level^2 / 2
> times. The reason of that is that when we found a bit in pidmap, we
> can't determine this pidns is top for this process or it isn't.
>
> vpid is a heavy operation, so a fork bomb, which create many nested
> namespace, can do a system inaccessible for a long time.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Signed-off-by: Andrew Vagin <avagin@...nvz.org>


Acked-by: Oleg Nesterov <oleg@...hat.com>



> ---
>  kernel/pid_namespace.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index b051fa6..598bfb3 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -70,12 +70,18 @@ err_alloc:
>  	return NULL;
>  }
>
> +/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
> +#define MAX_PID_NS_LEVEL 32
> +
>  static struct pid_namespace *create_pid_namespace(struct pid_namespace *parent_pid_ns)
>  {
>  	struct pid_namespace *ns;
>  	unsigned int level = parent_pid_ns->level + 1;
>  	int i, err = -ENOMEM;
>
> +	if (level > MAX_PID_NS_LEVEL)
> +		goto out;
> +
>  	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
>  	if (ns == NULL)
>  		goto out;
> --
> 1.7.1
>

--
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/