Bluetooth: L2CAP: Fix l2cap_global_chan_by_psm

jira VULN-206
cve CVE-2022-42896
commit-author Luiz Augusto von Dentz <[email protected]>
commit f937b75

l2cap_global_chan_by_psm shall not return fixed channels as they are not
meant to be connected by (S)PSM.

	Signed-off-by: Luiz Augusto von Dentz <[email protected]>
	Reviewed-by: Tedd Ho-Jeong An <[email protected]>
(cherry picked from commit f937b75)
	Signed-off-by: Marcin Wcisło <[email protected]>

Author: pvts-mat

net/bluetooth/l2cap_core.c

@@ -1960,7 +1960,7 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
 		if (link_type == LE_LINK && c->src_type == BDADDR_BREDR)
 			continue;
 
-		if (c->psm == psm) {
+		if (c->chan_type != L2CAP_CHAN_FIXED && c->psm == psm) {
 			int src_match, dst_match;
 			int src_any, dst_any;