netlink: add reference of module in netlink_dump_start

I get a panic when I use ss -a and rmmod inet_diag at the
same time.

It's because netlink_dump uses inet_diag_dump which belongs to module
inet_diag.

I search the codes and find many modules have the same problem.  We
need to add a reference to the module which the cb->dump belongs to.

Thanks for all help from Stephen,Jan,Eric,Steffen and Pablo.

Change From v3:
change netlink_dump_start to inline,suggestion from Pablo and
Eric.

Change From v2:
delete netlink_dump_done,and call module_put in netlink_dump
and netlink_sock_destruct.

Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 4 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index f80c56ac4d82..6d3af05c107c 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -245,6 +245,8 @@ struct netlink_callback {
                                         struct netlink_callback *cb);
         int                     (*done)(struct netlink_callback *cb);
         void                    *data;
+        /* the module that dump function belong to */
+        struct module           *module;
         u16                     family;
         u16                     min_dump_alloc;
         unsigned int            prev_seq, seq;
@@ -262,14 +264,24 @@ __nlmsg_put(struct sk_buff *skb, u32 portid, u32 seq, int type, int len, int fla
 
 struct netlink_dump_control {
         int (*dump)(struct sk_buff *skb, struct netlink_callback *);
-        int (*done)(struct netlink_callback*);
+        int (*done)(struct netlink_callback *);
         void *data;
+        struct module *module;
         u16 min_dump_alloc;
 };
 
-extern int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
-                              const struct nlmsghdr *nlh,
-                              struct netlink_dump_control *control);
+extern int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
+                                const struct nlmsghdr *nlh,
+                                struct netlink_dump_control *control);
+static inline int netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
+                                     const struct nlmsghdr *nlh,
+                                     struct netlink_dump_control *control)
+{
+        if (!control->module)
+                control->module = THIS_MODULE;
+
+        return __netlink_dump_start(ssk, skb, nlh, control);
+}
 
 #endif /* __KERNEL__ */