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>

diff --git a/net/tipc/monitor.c b/net/tipc/monitor.c
index b62caa1c770c042fa7449f401bcb333b3defa485..ed97a5876ebef128937906d4115d3c1db6d16998 100644 (file)
--- 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)