UBSAN reported those with MegaRAID SAS-3 3108,

[   77.467308] UBSAN: Undefined behaviour in drivers/scsi/megaraid/megaraid_sas_fp.c:117:32
[   77.475402] index 255 is out of range for type 'MR_LD_SPAN_MAP [1]'
[   77.481677] CPU: 16 PID: 333 Comm: kworker/16:1 Not tainted 4.20.0-rc5+ #1
[   77.488556] Hardware name: Huawei TaiShan 2280 /BC11SPCD, BIOS 1.50 06/01/2018
[   77.495791] Workqueue: events work_for_cpu_fn
[   77.500154] Call trace:
[   77.502610]  dump_backtrace+0x0/0x2c8
[   77.506279]  show_stack+0x24/0x30
[   77.509604]  dump_stack+0x118/0x19c
[   77.513098]  ubsan_epilogue+0x14/0x60
[   77.516765]  __ubsan_handle_out_of_bounds+0xfc/0x13c
[   77.521767]  mr_update_load_balance_params+0x150/0x158 [megaraid_sas]
[   77.528230]  MR_ValidateMapInfo+0x2cc/0x10d0 [megaraid_sas]
[   77.533825]  megasas_get_map_info+0x244/0x2f0 [megaraid_sas]
[   77.539505]  megasas_init_adapter_fusion+0x9b0/0xf48 [megaraid_sas]
[   77.545794]  megasas_init_fw+0x1ab4/0x3518 [megaraid_sas]
[   77.551212]  megasas_probe_one+0x2c4/0xbe0 [megaraid_sas]
[   77.556614]  local_pci_probe+0x7c/0xf0
[   77.560365]  work_for_cpu_fn+0x34/0x50
[   77.564118]  process_one_work+0x61c/0xf08
[   77.568129]  worker_thread+0x534/0xa70
[   77.571882]  kthread+0x1c8/0x1d0
[   77.575114]  ret_from_fork+0x10/0x1c

[   89.240332] UBSAN: Undefined behaviour in drivers/scsi/megaraid/megaraid_sas_fp.c:117:32
[   89.248426] index 255 is out of range for type 'MR_LD_SPAN_MAP [1]'
[   89.254700] CPU: 16 PID: 95 Comm: kworker/u130:0 Not tainted 4.20.0-rc5+ #1
[   89.261665] Hardware name: Huawei TaiShan 2280 /BC11SPCD, BIOS 1.50 06/01/2018
[   89.268903] Workqueue: events_unbound async_run_entry_fn
[   89.274222] Call trace:
[   89.276680]  dump_backtrace+0x0/0x2c8
[   89.280348]  show_stack+0x24/0x30
[   89.283671]  dump_stack+0x118/0x19c
[   89.287167]  ubsan_epilogue+0x14/0x60
[   89.290835]  __ubsan_handle_out_of_bounds+0xfc/0x13c
[   89.295828]  MR_LdRaidGet+0x50/0x58 [megaraid_sas]
[   89.300638]  megasas_build_io_fusion+0xbb8/0xd90 [megaraid_sas]
[   89.306576]  megasas_build_and_issue_cmd_fusion+0x138/0x460 [megaraid_sas]
[   89.313468]  megasas_queue_command+0x398/0x3d0 [megaraid_sas]
[   89.319222]  scsi_dispatch_cmd+0x1dc/0x8a8
[   89.323321]  scsi_request_fn+0x8e8/0xdd0
[   89.327249]  __blk_run_queue+0xc4/0x158
[   89.331090]  blk_execute_rq_nowait+0xf4/0x158
[   89.335449]  blk_execute_rq+0xdc/0x158
[   89.339202]  __scsi_execute+0x130/0x258
[   89.343041]  scsi_probe_and_add_lun+0x2fc/0x1488
[   89.347661]  __scsi_scan_target+0x1cc/0x8c8
[   89.351848]  scsi_scan_channel.part.3+0x8c/0xc0
[   89.356382]  scsi_scan_host_selected+0x130/0x1f0
[   89.361002]  do_scsi_scan_host+0xd8/0xf0
[   89.364927]  do_scan_async+0x9c/0x320
[   89.368594]  async_run_entry_fn+0x138/0x420
[   89.372780]  process_one_work+0x61c/0xf08
[   89.376793]  worker_thread+0x13c/0xa70
[   89.380546]  kthread+0x1c8/0x1d0
[   89.383778]  ret_from_fork+0x10/0x1c

This is because when populating Driver Map using firmware raid map, all
non-existing VDs set their ldTgtIdToLd to 0xff, so it can be skipped later.

From drivers/scsi/megaraid/megaraid_sas_base.c ,
memset(instance->ld_ids, 0xff, MEGASAS_MAX_LD_IDS);

From drivers/scsi/megaraid/megaraid_sas_fp.c ,
/* For non existing VDs, iterate to next VD*/
if (ld >= (MAX_LOGICAL_DRIVES_EXT - 1))
	continue;

However, there are a few places that failed to skip those non-existing VDs
due to off-by-one errors. Then, those 0xff leaked into MR_LdRaidGet(0xff,
map) and triggered the out-of-bound accesses.

Fixes: 51087a86 ("megaraid_sas : Extended VD support")
Signed-off-by: Qian Cai <cai@lca.pw>
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>