lkml.org 
[lkml]   [2012]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] pidns: limit the nesting depth of pid namespaces
From
2012/10/24 Andrew Morton <akpm@linux-foundation.org>:
> On Fri, 12 Oct 2012 16:30:42 +0400
> Andrew Vagin <avagin@openvz.org> 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.
>>
>> --- 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;
>
> hm, OK. This will kind-of fix the free_pid_ns()-excessive-recursion
> issue which we already fixed by other means ;)

I caught both problems with help of an one program, which create many
nested namespaces. Actually this patch prevents another problem. A few
thousand nested namespaces is destroyed for more than one minutes and
in this period a system is inaccessible.

>
> I don't think this problem is serious enough to bother backporting into
> -stable but I guess we can/should do it in 3.7. Agree?

Yes.

>
> I think that returning -ENOMEM in response to an excessive nesting
> attempt is misleading - the system *didn't* run out of memory. EINVAL
> is better?

I chose ENOMEM by analogy with max_pid. When a new PID can not be
allocated, ENOMEM is returned too.

>
>
>
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: pidns-limit-the-nesting-depth-of-pid-namespaces-fix
>
> return -EINVAL in response to excessive nesting, not -ENOMEM
>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Andrew Vagin <avagin@openvz.org>
> Cc: Cyrill Gorcunov <gorcunov@openvz.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Pavel Emelyanov <xemul@parallels.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> kernel/pid_namespace.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff -puN kernel/pid_namespace.c~pidns-limit-the-nesting-depth-of-pid-namespaces-fix kernel/pid_namespace.c
> --- a/kernel/pid_namespace.c~pidns-limit-the-nesting-depth-of-pid-namespaces-fix
> +++ a/kernel/pid_namespace.c
> @@ -78,11 +78,15 @@ static struct pid_namespace *create_pid_
> {
> struct pid_namespace *ns;
> unsigned int level = parent_pid_ns->level + 1;
> - int i, err = -ENOMEM;
> + int i;
> + int err;
>
> - if (level > MAX_PID_NS_LEVEL)
> + if (level > MAX_PID_NS_LEVEL) {
> + err = -EINVAL;
> goto out;
> + }
>
> + err = -ENOMEM;
> ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
> if (ns == NULL)
> goto out;
> _
>


\
 
 \ /
  Last update: 2012-10-24 08:21    [W:0.283 / U:0.284 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site