[patch v3 01/11] netlink: add reference of module in netlink_dump_start

[Gao feng]

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

it's because netlink_dump use inet_diag_dump witch function
belongs to module inet_diag.

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

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

Change From v2:

delete netlink_dump_done,and call module_put in netlink_dump
and netlink_sock_destruct.

Signed-off-by: Gao feng <gaof...@cn.fujitsu.com>
---
 include/linux/netlink.h  |    5 ++++-
 net/netlink/af_netlink.c |   21 +++++++++++++++++----
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index f80c56a..bf4e501 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;
@@ -262,8 +264,9 @@ __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;
 };
 
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0f2e3ad..0905dfb 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -169,6 +169,7 @@ static void netlink_sock_destruct(struct sock *sk)
        if (nlk->cb) {
                if (nlk->cb->done)
                        nlk->cb->done(nlk->cb);
+               module_put(nlk->cb->module);
                netlink_destroy_callback(nlk->cb);
        }
 
@@ -1755,6 +1756,8 @@ static int netlink_dump(struct sock *sk)
 
        if (cb->done)
                cb->done(cb);
+
+       module_put(cb->module);
        nlk->cb = NULL;
        mutex_unlock(nlk->cb_mutex);
 
@@ -1784,6 +1787,7 @@ int netlink_dump_start(struct sock *ssk, struct sk_buff 
*skb,
        cb->done = control->done;
        cb->nlh = nlh;
        cb->data = control->data;
+       cb->module = control->module;
        cb->min_dump_alloc = control->min_dump_alloc;
        atomic_inc(&skb->users);
        cb->skb = skb;
@@ -1794,19 +1798,28 @@ int netlink_dump_start(struct sock *ssk, struct sk_buff 
*skb,
                return -ECONNREFUSED;
        }
        nlk = nlk_sk(sk);
-       /* A dump is in progress... */
+
        mutex_lock(nlk->cb_mutex);
+       /* A dump is in progress... */
        if (nlk->cb) {
                mutex_unlock(nlk->cb_mutex);
                netlink_destroy_callback(cb);
-               sock_put(sk);
-               return -EBUSY;
+               ret = -EBUSY;
+               goto out;
        }
+       /* add reference of module witch cb->dump belong to */
+       if (!try_module_get(cb->module)) {
+               mutex_unlock(nlk->cb_mutex);
+               netlink_destroy_callback(cb);
+               ret = -EPROTONOSUPPORT;
+               goto out;
+       }
+
        nlk->cb = cb;
        mutex_unlock(nlk->cb_mutex);
 
        ret = netlink_dump(sk);
-
+out:
        sock_put(sk);
 
        if (ret)
-- 
1.7.7.6

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