Commit message: scsi: megaraid_sas: return error when create DMA pool failed

when create DMA pool for cmd frames failed, we should return -ENOMEM,
instead of 0.
In some case in:

    megasas_init_adapter_fusion()

    -->megasas_alloc_cmds()
       -->megasas_create_frame_pool
          create DMA pool failed,
        --> megasas_free_cmds() [1]

    -->megasas_alloc_cmds_fusion()
       failed, then goto fail_alloc_cmds.
    -->megasas_free_cmds() [2]

we will call megasas_free_cmds twice, [1] will kfree cmd_list,
[2] will use cmd_list.it will cause a problem:

Unable to handle kernel NULL pointer dereference at virtual address
00000000
pgd = ffffffc000f70000
[00000000] *pgd=0000001fbf893003, *pud=0000001fbf893003,
*pmd=0000001fbf894003, *pte=006000006d000707
Internal error: Oops: 96000005 [#1] SMP
 Modules linked in:
 CPU: 18 PID: 1 Comm: swapper/0 Not tainted
 task: ffffffdfb9290000 ti: ffffffdfb923c000 task.ti: ffffffdfb923c000
 PC is at megasas_free_cmds+0x30/0x70
 LR is at megasas_free_cmds+0x24/0x70
 ...
 Call trace:
 [<ffffffc0005b779c>] megasas_free_cmds+0x30/0x70
 [<ffffffc0005bca74>] megasas_init_adapter_fusion+0x2f4/0x4d8
 [<ffffffc0005b926c>] megasas_init_fw+0x2dc/0x760
 [<ffffffc0005b9ab0>] megasas_probe_one+0x3c0/0xcd8
 [<ffffffc0004a5abc>] local_pci_probe+0x4c/0xb4
 [<ffffffc0004a5c40>] pci_device_probe+0x11c/0x14c
 [<ffffffc00053a5e4>] driver_probe_device+0x1ec/0x430
 [<ffffffc00053a92c>] __driver_attach+0xa8/0xb0
 [<ffffffc000538178>] bus_for_each_dev+0x74/0xc8
  [<ffffffc000539e88>] driver_attach+0x28/0x34
 [<ffffffc000539a18>] bus_add_driver+0x16c/0x248
 [<ffffffc00053b234>] driver_register+0x6c/0x138
 [<ffffffc0004a5350>] __pci_register_driver+0x5c/0x6c
 [<ffffffc000ce3868>] megasas_init+0xc0/0x1a8
 [<ffffffc000082a58>] do_one_initcall+0xe8/0x1ec
 [<ffffffc000ca7be8>] kernel_init_freeable+0x1c8/0x284
 [<ffffffc0008d90b8>] kernel_init+0x1c/0xe4

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
CVE: CVE-2019-11810
CWE: CWE-476
Vulnerability description: An issue was discovered in the Linux kernel before 5.0.7. A NULL pointer dereference can occur when megasas_create_frame_pool() fails in megasas_alloc_cmds() in drivers/scsi/megaraid/megaraid_sas_base.c. This causes a Denial of Service, related to a use-after-free.

Project: linux
File: megaraid_sas_base.c

int megasas_alloc_cmds(struct megasas_instance *instance)
{
	int i;
	int j;
	u16 max_cmd;
	struct megasas_cmd *cmd;

	max_cmd = instance->max_mfi_cmds;

	/*
	 * instance->cmd_list is an array of struct megasas_cmd pointers.
	 * Allocate the dynamic array first and then allocate individual
	 * commands.
	 */
	instance->cmd_list = kcalloc(max_cmd, sizeof(struct megasas_cmd*), GFP_KERNEL);

	if (!instance->cmd_list) {
		dev_printk(KERN_DEBUG, &instance->pdev->dev, "out of memory\n");
		return -ENOMEM;
	}

	memset(instance->cmd_list, 0, sizeof(struct megasas_cmd *) *max_cmd);

	for (i = 0; i < max_cmd; i++) {
		instance->cmd_list[i] = kmalloc(sizeof(struct megasas_cmd),
						GFP_KERNEL);

		if (!instance->cmd_list[i]) {

			for (j = 0; j < i; j++)
				kfree(instance->cmd_list[j]);

			kfree(instance->cmd_list);
			instance->cmd_list = NULL;

			return -ENOMEM;
		}
	}

	for (i = 0; i < max_cmd; i++) {
		cmd = instance->cmd_list[i];
		memset(cmd, 0, sizeof(struct megasas_cmd));
		cmd->index = i;
		cmd->scmd = NULL;
		cmd->instance = instance;

		list_add_tail(&cmd->list, &instance->cmd_pool);
	}

	/*
	 * Create a frame pool and assign one frame to each cmd
	 */
 	if (megasas_create_frame_pool(instance)) {
 		dev_printk(KERN_DEBUG, &instance->pdev->dev, "Error creating frame DMA pool\n");
 		megasas_free_cmds(instance);
 	}
 
 	return 0;
}