Bluetooth: L2CAP: Fix l2cap_global_chan_by_psm regression

jira VULN-155527
cve-pre CVE-2022-50386
commit-author Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
commit 332f179

The patch d0be834: "Bluetooth: L2CAP: Fix use-after-free caused
by l2cap_chan_put" from Jul 21, 2022, leads to the following Smatch
static checker warning:

        net/bluetooth/l2cap_core.c:1977 l2cap_global_chan_by_psm()
        error: we previously assumed 'c' could be null (see line 1996)

Fixes: d0be834 ("Bluetooth: L2CAP: Fix use-after-free caused by l2cap_chan_put")
	Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
	Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
(cherry picked from commit 332f179)
	Signed-off-by: Brett Mastbergen <bmastbergen@ciq.com>

Author: bmastbergen

net/bluetooth/l2cap_core.c

@@ -1801,11 +1801,11 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
 						   bdaddr_t *dst,
 						   u8 link_type)
 {
-	struct l2cap_chan *c, *c1 = NULL;
+	struct l2cap_chan *c, *tmp, *c1 = NULL;
 
 	read_lock(&chan_list_lock);
 
-	list_for_each_entry(c, &chan_list, global_l) {
+	list_for_each_entry_safe(c, tmp, &chan_list, global_l) {
 		if (state && c->state != state)
 			continue;
 
@@ -1824,11 +1824,10 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
 			dst_match = !bacmp(&c->dst, dst);
 			if (src_match && dst_match) {
 				c = l2cap_chan_hold_unless_zero(c);
-				if (!c)
-					continue;
-
-				read_unlock(&chan_list_lock);
-				return c;
+				if (c) {
+					read_unlock(&chan_list_lock);
+					return c;
+				}
 			}
 
 			/* Closest match */