nvmet-tcp: fix NULL pointer dereference during release

nvmet-tcp frees CMD buffers in nvmet_tcp_uninit_data_in_cmds(),
and waits the inflight IO requests in nvmet_sq_destroy(). During wait
the inflight IO requests, the callback nvmet_tcp_queue_response()
is called from backend after IO complete, this leads a typical
Use-After-Free issue like this:

 BUG: kernel NULL pointer dereference, address: 0000000000000008
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 107f80067 P4D 107f80067 PUD 10789e067 PMD 0
 Oops: 0000 [#1] PREEMPT SMP NOPTI
 CPU: 1 PID: 123 Comm: kworker/1:1H Kdump: loaded Tainted: G            E      6.0.0-rc2.bm.1-amd64 #15
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
 Workqueue: nvmet_tcp_wq nvmet_tcp_io_work [nvmet_tcp]
 RIP: 0010:shash_ahash_digest+0x2b/0x110
 Code: 1f 44 00 00 41 57 41 56 41 55 41 54 55 48 89 fd 53 48 89 f3 48 83 ec 08 44 8b 67 30 45 85 e4 74 1c 48 8b 57 38 b8 00 10 00 00 <44> 8b 7a 08 44 29 f8 39 42 0c 0f 46 42 0c 41 39 c4 76 43 48 8b 03
 RSP: 0018:ffffc9000051bdd8 EFLAGS: 00010206
 RAX: 0000000000001000 RBX: ffff888100ab5470 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: ffff888100ab5470 RDI: ffff888100ab5420
 RBP: ffff888100ab5420 R08: ffff8881024d08c8 R09: ffff888103e1b4b8
 R10: 8080808080808080 R11: 0000000000000000 R12: 0000000000001000
 R13: 0000000000000000 R14: ffff88813412bd4c R15: ffff8881024d0800
 FS:  0000000000000000(0000) GS:ffff88883fa40000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000008 CR3: 0000000104b48000 CR4: 0000000000350ee0
 Call Trace:
  <TASK>
  nvmet_tcp_io_work+0xa52/0xb52 [nvmet_tcp]
  ? __switch_to+0x106/0x420
  process_one_work+0x1ae/0x380
  ? process_one_work+0x380/0x380
  worker_thread+0x30/0x360
  ? process_one_work+0x380/0x380
  kthread+0xe6/0x110
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x1f/0x30

Separate nvmet_tcp_uninit_data_in_cmds() into two steps:

  uninit data in cmds                  <- new step 1
  nvmet_sq_destroy();
  cancel_work_sync(&queue->io_work);
  free CMD buffers                     <- new step 2
Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/tcp.c

@@ -1406,16 +1406,28 @@ static void nvmet_tcp_uninit_data_in_cmds(struct nvmet_tcp_queue *queue)
 	for (i = 0; i < queue->nr_cmds; i++, cmd++) {
 		if (nvmet_tcp_need_data_in(cmd))
 			nvmet_req_uninit(&cmd->req);
-
-		nvmet_tcp_free_cmd_buffers(cmd);
 	}
 
 	if (!queue->nr_cmds && nvmet_tcp_need_data_in(&queue->connect)) {
 		/* failed in connect */
-		nvmet_tcp_finish_cmd(&queue->connect);
+		nvmet_req_uninit(&queue->connect.req);
 	}
 }
 
+static void nvmet_tcp_free_cmd_data_in_buffers(struct nvmet_tcp_queue *queue)
+{
+	struct nvmet_tcp_cmd *cmd = queue->cmds;
+	int i;
+
+	for (i = 0; i < queue->nr_cmds; i++, cmd++) {
+		if (nvmet_tcp_need_data_in(cmd))
+			nvmet_tcp_free_cmd_buffers(cmd);
+	}
+
+	if (!queue->nr_cmds && nvmet_tcp_need_data_in(&queue->connect))
+		nvmet_tcp_free_cmd_buffers(&queue->connect);
+}
+
 static void nvmet_tcp_release_queue_work(struct work_struct *w)
 {
 	struct page *page;
@@ -1434,6 +1446,7 @@ static void nvmet_tcp_release_queue_work(struct work_struct *w)
 	nvmet_tcp_uninit_data_in_cmds(queue);
 	nvmet_sq_destroy(&queue->nvme_sq);
 	cancel_work_sync(&queue->io_work);
+	nvmet_tcp_free_cmd_data_in_buffers(queue);
 	sock_release(queue->sock);
 	nvmet_tcp_free_cmds(queue);
 	if (queue->hdr_digest || queue->data_digest)