Messages in this thread Patch in this message | | | From | Andrew Vagin <> | Subject | [PATCH] pidns: limit a size of pid to one page | Date | Wed, 10 Oct 2012 14:24:14 +0400 |
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A size of pid depends on a level of pidns and now a level of pidns is not limited, so it can be more than one page.
Looks reasonable, that it should be limited to a page size. On x86_64 it will allow to create 125 nested pid namespaces. I don't know a usecase for which, it will be not enough. 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.
For example my system becomes inaccessible for a few minutes with 4000 processes.
Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Pavel Emelyanov <xemul@parallels.com> Signed-off-by: Andrew Vagin <avagin@openvz.org> --- 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..bc822e6 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -70,12 +70,18 @@ err_alloc: return NULL; } +/* Limit a size of pid to one page */ +#define MAX_PID_NS_LEVEL ((PAGE_SIZE - sizeof(struct pid)) / sizeof(struct upid)) + 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
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