tipc: fix variable dereference before NULL check

In commit cf6f7e1d5109 ("tipc: dump monitor attributes"),
I dereferenced a pointer before checking if its valid.
This is reported by static check Smatch as:
net/tipc/monitor.c:733 tipc_nl_add_monitor_peer()
     warn: variable dereferenced before check 'mon' (see line 731)

In this commit, we check for a valid monitor before proceeding
with any other operation.

Fixes: cf6f7e1d5109 ("tipc: dump monitor attributes")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/tipc/monitor.c b/net/tipc/monitor.c
index b62caa1c770c..ed97a5876ebe 100644
--- a/net/tipc/monitor.c
+++ b/net/tipc/monitor.c
@@ -728,12 +728,13 @@ int tipc_nl_add_monitor_peer(struct net *net, struct tipc_nl_msg *msg,
                              u32 bearer_id, u32 *prev_node)
 {
         struct tipc_monitor *mon = tipc_monitor(net, bearer_id);
-        struct tipc_peer *peer = mon->self;
+        struct tipc_peer *peer;
 
         if (!mon)
                 return -EINVAL;
 
         read_lock_bh(&mon->lock);
+        peer = mon->self;
         do {
                 if (*prev_node) {
                         if (peer->addr == *prev_node)