Re: [PATCH] inet_diag: fix panic when unload inet_diag

于 2012年09月25日 14:36, Eric Dumazet 写道:

On Tue, 2012-09-25 at 10:48 +0800, Gao feng wrote:

quoted

when inet_diag being compiled as module, inet_diag_handler_dump
set netlink_dump_control.dump to inet_diag_dump,so if module
inet_diag is unloaded,netlink will still try to call this function
in netlink_dump. this will cause kernel panic.

fix this by adding a reference of inet_diag module before
setting netlink_callback, and release this reference in
netlink_callback.done.

Thanks for all help from Stephen,Jan and Eric.

...

quoted

@@ -1001,8 +1025,26 @@ static int inet_diag_handler_dump(struct sk_buff *skb, struct nlmsghdr *h)
 		{
 			struct netlink_dump_control c = {
 				.dump = inet_diag_dump,
+				.done = inet_diag_done,
 			};
-			return netlink_dump_start(net->diag_nlsk, skb, h, &c);
+			int err;
+			/*
+			 * netlink_dump will call inet_diag_dump,
+			 * so we need a reference of THIS_MODULE.
+			 */
+			if (!try_module_get(THIS_MODULE))
+				return -EPROTONOSUPPORT;
+
+			err = netlink_dump_start(net->diag_nlsk, skb, h, &c);
+
+			if ((err != -EINTR) && (err != -ENOBUFS)) {
+				/*
+				 * netlink_callback set failed, release the
+				 * referenct of THIS_MODULE.
+				 */
+				module_put(THIS_MODULE);
+			}
+			return err;
 		}
 	}
 

Hmm... this seems error prone...

In the future, netlink_dump_start() could be changed to return other
errors than EINTR or ENOBUFS that need the module_put()

EINTR and ENOBUFS is returned by netlink_dump, netlink_dump is called by
netlink_dump_start after netlink_callback being set successfully.
so this checking of EINTR and ENOBUFS here is to determinate if we set
netlink_callback successfully.

I think in order to reduce error prone,we have to change netlink_dump_start
to determinate if we set netlink_callback successfully.

I would change netlink_dump_start() to __netlink_dump_start() and add a
module param to it, so that this module stuff is centralized in
__netlink_dump_start()

Then, instead of calling (from inet_diag)

netlink_dump_start(net->diag_nlsk, skb, nlh, &c);

you would use :

__netlink_dump_start(net->diag_nlsk, skb, nlh, &c, THIS_MODULE);

I wonder if this fix is not needed elsewhere eventually
(net/unix/af_unix.c for example ?)

do you mean net/unix/unix_diag.c ?
I test nfnetlink module,it has the same problem.

It's need to modify netlink_dump_start not only wrap netlink_dump_start.