From 53286ba0cf56585048b5363844dec924081fe06d Mon Sep 17 00:00:00 2001 From: Andrew Vagin Date: Wed, 10 Oct 2012 12:22:16 +0400 Subject: [PATCH] pidns: limit the nesting depth of pid namespaces (v2) '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. v2: return EINVAL in response to an excessive nesting attempt Cc: Andrew Morton Cc: Oleg Nesterov Cc: Cyrill Gorcunov Cc: "Eric W. Biederman" Cc: Pavel Emelyanov Signed-off-by: Andrew Vagin --- 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 478bad2..c923bb5 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -71,12 +71,18 @@ 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) + return ERR_PTR(-EINVAL); + ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL); if (ns == NULL) goto out; -- 1.7.1