[Patch net] tipc: call start and done ops directly in __tipc_nl_compat_dumpit()

[Cong Wang <xiyou.wangcong@gmail.com>]

__tipc_nl_compat_dumpit() uses a netlink_callback on stack,
so the only way to align it with other ->dumpit() call path
is calling tipc_dump_start() and tipc_dump_done() directly
inside it. Otherwise ->dumpit() would always get NULL from
cb->args[0].

But, tipc_dump_start() uses sock_net(cb->skb->sk) to retrieve
net pointer, the cb->skb here doesn't set ->sk, the net pointer
is saved in msg->net instead, so introduce a helper function
__tipc_dump_start() to pass in msg->net.

Fixes: 9a07efa9aea2 ("tipc: switch to rhashtable iterator")
Reported-by: syzbot+e93a2c41f91b8e2c7d9b@syzkaller.appspotmail.com
Cc: Jon Maloy <jon.maloy@ericsson.com>
Cc: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 net/tipc/netlink_compat.c | 2 ++
 net/tipc/socket.c         | 8 ++++++--
 net/tipc/socket.h         | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/tipc/netlink_compat.c b/net/tipc/netlink_compat.c
index a2f76743c73a..82f665728382 100644
--- a/net/tipc/netlink_compat.c
+++ b/net/tipc/netlink_compat.c
@@ -185,6 +185,7 @@ static int __tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
 		return -ENOMEM;
 
 	buf->sk = msg->dst_sk;
+	__tipc_dump_start(&cb, msg->net);
 
 	do {
 		int rem;
@@ -216,6 +217,7 @@ static int __tipc_nl_compat_dumpit(struct tipc_nl_compat_cmd_dump *cmd,
 	err = 0;
 
 err_out:
+	tipc_dump_done(&cb);
 	kfree_skb(buf);
 
 	if (err == -EMSGSIZE) {
diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index ab7a2a7178f7..a19b2b1c77ed 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -3264,9 +3264,14 @@ int tipc_nl_sk_walk(struct sk_buff *skb, struct netlink_callback *cb,
 EXPORT_SYMBOL(tipc_nl_sk_walk);
 
 int tipc_dump_start(struct netlink_callback *cb)
+{
+	return __tipc_dump_start(cb, sock_net(cb->skb->sk));
+}
+EXPORT_SYMBOL(tipc_dump_start);
+
+int __tipc_dump_start(struct netlink_callback *cb, struct net *net)
 {
 	struct rhashtable_iter *iter = (void *)cb->args[0];
-	struct net *net = sock_net(cb->skb->sk);
 	struct tipc_net *tn = tipc_net(net);
 
 	if (!iter) {
@@ -3280,7 +3285,6 @@ int tipc_dump_start(struct netlink_callback *cb)
 	rhashtable_walk_enter(&tn->sk_rht, iter);
 	return 0;
 }
-EXPORT_SYMBOL(tipc_dump_start);
 
 int tipc_dump_done(struct netlink_callback *cb)
 {
diff --git a/net/tipc/socket.h b/net/tipc/socket.h
index d43032e26532..5e575f205afe 100644
--- a/net/tipc/socket.h
+++ b/net/tipc/socket.h
@@ -69,5 +69,6 @@ int tipc_nl_sk_walk(struct sk_buff *skb, struct netlink_callback *cb,
 				       struct netlink_callback *cb,
 				       struct tipc_sock *tsk));
 int tipc_dump_start(struct netlink_callback *cb);
+int __tipc_dump_start(struct netlink_callback *cb, struct net *net);
 int tipc_dump_done(struct netlink_callback *cb);
 #endif
-- 
2.14.4