Re: [PATCH v2 03/12] scsi: mpt3sas: Make MPI2_CONFIG_PAGE_RAID_VOL_0::PhysDisk[] a flexible array

[Kees Cook <keescook@chromium.org>]

On Sun, Aug 06, 2023 at 10:05:55AM -0700, James Seo wrote:
> This terminal 1-length variable array can be directly converted into
> a C99 flexible array member.
> 
> As all users of MPI2_CONFIG_PAGE_RAID_VOL_0 (Mpi2RaidVolPage0_t)
> either calculate its size without depending on its sizeof() or do not
> use PhysDisk[], no further source changes are required:

Tons of binary changes in this file too. I see this:

        Mpi2RaidVolPage0_t config_page;
	...
        r = _config_request(ioc, &mpi_request, &mpi_reply,
            MPT3_CONFIG_PAGE_DEFAULT_TIMEOUT, &config_page,
            sizeof(Mpi2RaidVolPage0_t));

So it's already changing this size (and possibly under-allocating now).

> - mpt3sas_config.c:mpt3sas_config_get_number_pds() fetches a
>   Mpi2RaidVolPage0_t for itself, but does not use PhysDisk[].

Is it certain that _config_request()'s use of mpt3sas_wait_for_ioc()
won't result in the hardware being upset that config_page_sz shrank?

> @@ -1826,8 +1823,7 @@ typedef struct _MPI2_CONFIG_PAGE_RAID_VOL_0 {
>  	U8                      Reserved2;         /*0x25 */
>  	U8                      Reserved3;         /*0x26 */
>  	U8                      InactiveStatus;    /*0x27 */
> -	MPI2_RAIDVOL0_PHYS_DISK
> -	PhysDisk[MPI2_RAID_VOL_PAGE_0_PHYSDISK_MAX]; /*0x28 */
> +	MPI2_RAIDVOL0_PHYS_DISK PhysDisk[];        /*0x28 */
>  } MPI2_CONFIG_PAGE_RAID_VOL_0,

Without the mpt3sas maintainers chiming in on this, I think the only
safe changes to make here are those with 0 binary differences. So for
things like this, it'll need to be:

-	MPI2_RAIDVOL0_PHYS_DISK
-	PhysDisk[MPI2_RAID_VOL_PAGE_0_PHYSDISK_MAX]; /*0x28 */
+	union {
+		MPI2_RAIDVOL0_PHYS_DISK legacy_padding;        /*0x28 */
+		DECLARE_FLEX_ARRAY(MPI2_RAIDVOL0_PHYS_DISK, PhysDisk);
+	};

-- 
Kees Cook