net: caif: clear client service pointer on teardown

commit f7cf8ec upstream.

`caif_connect()` can tear down an existing client after remote shutdown by
calling `caif_disconnect_client()` followed by `caif_free_client()`.
`caif_free_client()` releases the service layer referenced by
`adap_layer->dn`, but leaves that pointer stale.

When the socket is later destroyed, `caif_sock_destructor()` calls
`caif_free_client()` again and dereferences the freed service pointer.

Clear the client/service links before releasing the service object so
repeated teardown becomes harmless.

Fixes: 43e3692 ("caif: Move refcount from service layer to sock and dev.")
Cc: stable@kernel.org
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Tested-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Zhengchuan Liang <zcliangcn@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Link: https://patch.msgid.link/9f3d37847c0037568aae698ca23cd47c6691acb0.1775897577.git.zcliangcn@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ARC-CPS

net/caif/cfsrvl.c

@@ -197,10 +197,20 @@ bool cfsrvl_phyid_match(struct cflayer *layer, int phyid)
 
 void caif_free_client(struct cflayer *adap_layer)
 {
+	struct cflayer *serv_layer;
 	struct cfsrvl *servl;
-	if (adap_layer == NULL || adap_layer->dn == NULL)
+
+	if (!adap_layer)
+		return;
+
+	serv_layer = adap_layer->dn;
+	if (!serv_layer)
 		return;
-	servl = container_obj(adap_layer->dn);
+
+	layer_set_dn(adap_layer, NULL);
+	layer_set_up(serv_layer, NULL);
+
+	servl = container_obj(serv_layer);
 	servl->release(&servl->layer);
 }
 EXPORT_SYMBOL(caif_free_client);