tipc: use the right skb in tipc_sk_fill_sock_diag()

Commit 4b2e687 ("tipc: Fix namespace violation in tipc_sk_fill_sock_diag")
tried to fix the crash but failed, the crash is still 100% reproducible
with it.

In tipc_sk_fill_sock_diag(), skb is the diag dump we are filling, it is not
correct to retrieve its NETLINK_CB(), instead, like other protocol diag,
we should use NETLINK_CB(cb->skb).sk here.

Reported-by: <syzbot+326e587eff1074657718@syzkaller.appspotmail.com>
Fixes: 4b2e687 ("tipc: Fix namespace violation in tipc_sk_fill_sock_diag")
Fixes: c30b70d (tipc: implement socket diagnostics for AF_TIPC)
Cc: GhantaKrishnamurthy MohanKrishna <mohan.krishna.ghanta.krishnamurthy@ericsson.com>
Cc: Jon Maloy <jon.maloy@ericsson.com>
Cc: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/diag.c

@@ -59,7 +59,7 @@ static int __tipc_add_sock_diag(struct sk_buff *skb,
 	if (!nlh)
 		return -EMSGSIZE;
 
-	err = tipc_sk_fill_sock_diag(skb, tsk, req->tidiag_states,
+	err = tipc_sk_fill_sock_diag(skb, cb, tsk, req->tidiag_states,
 				     __tipc_diag_gen_cookie);
 	if (err)
 		return err;

net/tipc/socket.c

@@ -3257,8 +3257,8 @@ int tipc_nl_sk_walk(struct sk_buff *skb, struct netlink_callback *cb,
 }
 EXPORT_SYMBOL(tipc_nl_sk_walk);
 
-int tipc_sk_fill_sock_diag(struct sk_buff *skb, struct tipc_sock *tsk,
-			   u32 sk_filter_state,
+int tipc_sk_fill_sock_diag(struct sk_buff *skb, struct netlink_callback *cb,
+			   struct tipc_sock *tsk, u32 sk_filter_state,
 			   u64 (*tipc_diag_gen_cookie)(struct sock *sk))
 {
 	struct sock *sk = &tsk->sk;
@@ -3280,7 +3280,7 @@ int tipc_sk_fill_sock_diag(struct sk_buff *skb, struct tipc_sock *tsk,
 	    nla_put_u32(skb, TIPC_NLA_SOCK_TIPC_STATE, (u32)sk->sk_state) ||
 	    nla_put_u32(skb, TIPC_NLA_SOCK_INO, sock_i_ino(sk)) ||
 	    nla_put_u32(skb, TIPC_NLA_SOCK_UID,
-			from_kuid_munged(sk_user_ns(NETLINK_CB(skb).sk),
+			from_kuid_munged(sk_user_ns(NETLINK_CB(cb->skb).sk),
 					 sock_i_uid(sk))) ||
 	    nla_put_u64_64bit(skb, TIPC_NLA_SOCK_COOKIE,
 			      tipc_diag_gen_cookie(sk),

net/tipc/socket.h

@@ -61,8 +61,8 @@ int tipc_sk_rht_init(struct net *net);
 void tipc_sk_rht_destroy(struct net *net);
 int tipc_nl_sk_dump(struct sk_buff *skb, struct netlink_callback *cb);
 int tipc_nl_publ_dump(struct sk_buff *skb, struct netlink_callback *cb);
-int tipc_sk_fill_sock_diag(struct sk_buff *skb, struct tipc_sock *tsk,
-			   u32 sk_filter_state,
+int tipc_sk_fill_sock_diag(struct sk_buff *skb, struct netlink_callback *cb,
+			   struct tipc_sock *tsk, u32 sk_filter_state,
 			   u64 (*tipc_diag_gen_cookie)(struct sock *sk));
 int tipc_nl_sk_walk(struct sk_buff *skb, struct netlink_callback *cb,
 		    int (*skb_handler)(struct sk_buff *skb,