ocfs2/cluster: keep heartbeat local node stable

In the Linux kernel, the following vulnerability has been resolved: ocfs2/cluster: keep heartbeat local node stable o2nm_node_local_store() handles local=0 by stopping o2net and setting cl_local_node to O2NM_INVALID_NODE_NUM, but it leaves cl_has_local set. That stale state makes o2nm_this_node() return 255, blocks a later local=1 attempt with -EBUSY, and can feed 255 to heartbeat users that call o2nm_this_node() dynamically. Clearing cl_has_local is required when the local node is reset. But heartbeat threads can still be running at that point. They pin the local node config item at startup, yet o2hb_do_disk_heartbeat() and thread teardown re-read o2nm_this_node() for the local slot and for o2nm_undepend_this_node(). Once local=0 has cleared the live local-node state, those dynamic reads return O2NM_MAX_NODES, which is also the invalid node number 255. Store the local node number in the heartbeat region when the region starts. Use that stable node for heartbeat slot writes/checks, negotiation messages, and the final configfs undepend. Stop the heartbeat loop when the current local node no longer matches the stored node, and clear cl_has_local together with cl_local_node in the local=0 path so nodemanager state matches node removal. Validation reproduced this kernel report: KASAN slab-out-of-bounds in o2hb_do_disk_heartbeat+0x372/0xb30 RIP: 0010:memset+0xf/0x20 Read of size 8 Call trace: dump_stack_lvl+0x66/0xa0 print_report+0xd0/0x630 o2hb_do_disk_heartbeat+0x372/0xb30 (fs/ocfs2/cluster/heartbeat.c:1079) srso_alias_return_thunk+0x5/0xfbef5 __virt_addr_valid+0x188/0x2f0 kasan_report+0xe4/0x120 o2hb_do_disk_heartbeat+0x5/0xb30 (fs/ocfs2/cluster/heartbeat.c:1079) o2hb_thread+0x14e/0x770 kthread_affine_node+0x139/0x180 lockdep_hardirqs_on_prepare+0xda/0x190 trace_hardirqs_on+0x18/0x130 kthread+0x19d/0x1e0 ret_from_fork+0x37a/0x4d0 __switch_to+0x2d5/0x6f0 ret_from_fork_asm+0x1a/0x30