path: root/kernel/pid_namespace.c
diff options
authorAndrew Vagin <avagin@openvz.org>2012-10-25 13:38:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-25 14:37:53 -0700
commitf2302505775fd13ba93f034206f1e2a587017929 (patch)
tree0397e3cbf7556e93618ed7ad7316578049707ca1 /kernel/pid_namespace.c
parentd5ea7b5ec1ee4dac868143806c0bd94855754677 (diff)
pidns: limit the nesting depth of pid namespaces
'struct pid' is a "variable sized struct" - a header with an array of upids at the end. The 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 the 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 make a system inaccessible for a long time. For example my system becomes inaccessible for a few minutes with 4000 processes. [akpm@linux-foundation.org: return -EINVAL in response to excessive nesting, not -ENOMEM] Signed-off-by: Andrew Vagin <avagin@openvz.org> Acked-by: 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 Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/pid_namespace.c')
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index eb00be20581..7b07cc0dfb7 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -71,12 +71,22 @@ 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;
+ int i;
+ int err;
+ 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;