Re: [PATCH v2 3/4][next] scsi: megaraid_sas: Replace one-element array with flexible-array member in MR_DRV_RAID_MAP

Kees Cook
2022-06-22T22:26:46Z

On Wed, Aug 04, 2021 at 11:20:04PM -0500, Gustavo A. R. Silva wrote:
> Replace one-element array with a flexible-array member in struct
> MR_DRV_RAID_MAP and use the flex_array_size() helper.
>
> This helps with the ongoing efforts to globally enable -Warray-bounds
> and get us closer to being able to tighten the FORTIFY_SOURCE routines
> on memcpy().
>
> Link: https://en.wikipedia.org/wiki/Flexible_array_member
> Link: https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

I'd really like to see this fixed. :) I'm running into this 1-element
array problem now with UBSAN_BOUNDS:

[ 10.011173] UBSAN: array-index-out-of-bounds in /build/linux-WLUive/linux-5.15.0/drivers/scsi/megaraid/megaraid_sas_fp.c:103:32
[ 10.087824] index 1 is out of range for type 'MR_LD_SPAN_MAP [1]'

and I'm not the only one:

https://bugzilla.kernel.org/show_bug.cgi?id=215943

> ---
> Changes in v2:
> - None.
>
> drivers/scsi/megaraid/megaraid_sas_fp.c | 6 +++---
> drivers/scsi/megaraid/megaraid_sas_fusion.h | 2 +-
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/scsi/megaraid/megaraid_sas_fp.c b/drivers/scsi/megaraid/megaraid_sas_fp.c
> index da1cad1ee123..9cb36ef96c2c 100644
> --- a/drivers/scsi/megaraid/megaraid_sas_fp.c
> +++ b/drivers/scsi/megaraid/megaraid_sas_fp.c
> @@ -229,8 +229,8 @@ static int MR_PopulateDrvRaidMap(struct megasas_instance *instance, u64 map_id)
> le32_to_cpu(desc_table->raid_map_desc_offset));
> memcpy(pDrvRaidMap->ldSpanMap,
> fw_map_dyn->ld_span_map,
> - sizeof(struct MR_LD_SPAN_MAP) *
> - le32_to_cpu(desc_table->raid_map_desc_elements));
> + flex_array_size(pDrvRaidMap, ldSpanMap,
> + le32_to_cpu(desc_table->raid_map_desc_elements)));
> break;
> default:
> dev_dbg(&instance->pdev->dev, "wrong number of desctableElements %d\n",
> @@ -254,7 +254,7 @@ static int MR_PopulateDrvRaidMap(struct megasas_instance *instance, u64 map_id)
> pDrvRaidMap->ldTgtIdToLd[i] =
> (u16)fw_map_ext->ldTgtIdToLd[i];
> memcpy(pDrvRaidMap->ldSpanMap, fw_map_ext->ldSpanMap,
> - sizeof(struct MR_LD_SPAN_MAP) * ld_count);
> + flex_array_size(pDrvRaidMap, ldSpanMap, ld_count));
> memcpy(pDrvRaidMap->arMapInfo, fw_map_ext->arMapInfo,
> sizeof(struct MR_ARRAY_INFO) * MAX_API_ARRAYS_EXT);
> memcpy(pDrvRaidMap->devHndlInfo, fw_map_ext->devHndlInfo,
> diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.h b/drivers/scsi/megaraid/megaraid_sas_fusion.h
> index 9adb8b30f422..5fe2f7a6eebe 100644
> --- a/drivers/scsi/megaraid/megaraid_sas_fusion.h
> +++ b/drivers/scsi/megaraid/megaraid_sas_fusion.h
> @@ -1182,7 +1182,7 @@ struct MR_DRV_RAID_MAP {
> devHndlInfo[MAX_RAIDMAP_PHYSICAL_DEVICES_DYN];
> u16 ldTgtIdToLd[MAX_LOGICAL_DRIVES_DYN];
> struct MR_ARRAY_INFO arMapInfo[MAX_API_ARRAYS_DYN];
> - struct MR_LD_SPAN_MAP ldSpanMap[1];
> + struct MR_LD_SPAN_MAP ldSpanMap[];
>
> };
>

I think this patch is incomplete, and the wrapping struct needs to be
adjusted too:

@@ -1193,7 +1193,7 @@ struct MR_DRV_RAID_MAP {
struct MR_DRV_RAID_MAP_ALL {

struct MR_DRV_RAID_MAP raidMap;
- struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN - 1];
+ struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN];
} __packed;

With that added, I get zero changes to the executable code.

I assume the others need adjustment too.

--
Kees Cook