'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 <a...@linux-foundation.org>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Cyrill Gorcunov <gorcu...@openvz.org>
Cc: "Eric W. Biederman" <ebied...@xmission.com>
Cc: Pavel Emelyanov <xe...@parallels.com>
Signed-off-by: Andrew Vagin <ava...@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..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
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