Bluetooth: L2CAP: Fix l2cap_global_chan_by_psm regression

stable inclusion
from stable-v4.19.256
commit a55ac4419fb75295386e9cd386ab34b62b18e869
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I64WCC
CVE: CVE-2022-20566

--------------------------------

commit 332f1795 upstream.

The patch d0be8347: "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: d0be8347 ("Bluetooth: L2CAP: Fix use-after-free caused by l2cap_chan_put")
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NLuiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NLu Jialin <lujialin4@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Reviewed-by: NWang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

net/bluetooth/l2cap_core.c

@@ -1797,11 +1797,11 @@ 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;
 
@@ -1820,11 +1820,10 @@ 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 */