nvme-core: fix memory leak in dhchap_secret_store

Free dhchap_secret in nvme_ctrl_dhchap_secret_store() before we return
fix following kmemleack:-

unreferenced object 0xffff8886376ea800 (size 64):
  comm "check", pid 22048, jiffies 4344316705 (age 92.199s)
  hex dump (first 32 bytes):
    44 48 48 43 2d 31 3a 30 30 3a 6e 78 72 35 4b 67  DHHC-1:00:nxr5Kg
    75 58 34 75 6f 41 78 73 4a 61 34 63 2f 68 75 4c  uX4uoAxsJa4c/huL
  backtrace:
    [<0000000030ce5d4b>] __kmalloc+0x4b/0x130
    [<000000009be1cdc1>] nvme_ctrl_dhchap_secret_store+0x8f/0x160 [nvme_core]
    [<00000000ac06c96a>] kernfs_fop_write_iter+0x12b/0x1c0
    [<00000000437e7ced>] vfs_write+0x2ba/0x3c0
    [<00000000f9491baf>] ksys_write+0x5f/0xe0
    [<000000001c46513d>] do_syscall_64+0x3b/0x90
    [<00000000ecf348fe>] entry_SYSCALL_64_after_hwframe+0x72/0xdc
unreferenced object 0xffff8886376eaf00 (size 64):
  comm "check", pid 22048, jiffies 4344316736 (age 92.168s)
  hex dump (first 32 bytes):
    44 48 48 43 2d 31 3a 30 30 3a 6e 78 72 35 4b 67  DHHC-1:00:nxr5Kg
    75 58 34 75 6f 41 78 73 4a 61 34 63 2f 68 75 4c  uX4uoAxsJa4c/huL
  backtrace:
    [<0000000030ce5d4b>] __kmalloc+0x4b/0x130
    [<000000009be1cdc1>] nvme_ctrl_dhchap_secret_store+0x8f/0x160 [nvme_core]
    [<00000000ac06c96a>] kernfs_fop_write_iter+0x12b/0x1c0
    [<00000000437e7ced>] vfs_write+0x2ba/0x3c0
    [<00000000f9491baf>] ksys_write+0x5f/0xe0
    [<000000001c46513d>] do_syscall_64+0x3b/0x90
    [<00000000ecf348fe>] entry_SYSCALL_64_after_hwframe+0x72/0xdc

Fixes: f50fff73 ("nvme: implement In-Band authentication")
Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/core.c

@@ -3825,8 +3825,10 @@ static ssize_t nvme_ctrl_dhchap_secret_store(struct device *dev,
 		int ret;
 
 		ret = nvme_auth_generate_key(dhchap_secret, &key);
-		if (ret)
+		if (ret) {
+			kfree(dhchap_secret);
 			return ret;
+		}
 		kfree(opts->dhchap_secret);
 		opts->dhchap_secret = dhchap_secret;
 		host_key = ctrl->host_key;
@@ -3834,7 +3836,8 @@ static ssize_t nvme_ctrl_dhchap_secret_store(struct device *dev,
 		ctrl->host_key = key;
 		mutex_unlock(&ctrl->dhchap_auth_mutex);
 		nvme_auth_free_key(host_key);
-	}
+	} else
+		kfree(dhchap_secret);
 	/* Start re-authentication */
 	dev_info(ctrl->device, "re-authenticating controller\n");
 	queue_work(nvme_wq, &ctrl->dhchap_auth_work);