dm raid: fix address sanitizer warning in raid_status

In the Linux kernel, the following vulnerability has been resolved:

dm raid: fix address sanitizer warning in raid_status

There is this warning when using a kernel with the address sanitizer

and running this testsuite:

https://gitlab.com/cki-project/kernel-tests/-/tree/main/storage/swraid/scsi_raid

==================================================================

BUG: KASAN: slab-out-of-bounds in raid_status+0x1747/0x2820 [dm_raid]

Read of size 4 at addr ffff888079d2c7e8 by task lvcreate/13319

CPU: 0 PID: 13319 Comm: lvcreate Not tainted 5.18.0-0.rc3.<snip> #1

Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011

Call Trace:

<TASK>

dump_stack_lvl+0x6a/0x9c

print_address_description.constprop.0+0x1f/0x1e0

print_report.cold+0x55/0x244

kasan_report+0xc9/0x100

raid_status+0x1747/0x2820 [dm_raid]

dm_ima_measure_on_table_load+0x4b8/0xca0 [dm_mod]

table_load+0x35c/0x630 [dm_mod]

ctl_ioctl+0x411/0x630 [dm_mod]

dm_ctl_ioctl+0xa/0x10 [dm_mod]

__x64_sys_ioctl+0x12a/0x1a0

do_syscall_64+0x5b/0x80

The warning is caused by reading conf->max_nr_stripes in raid_status. The

code in raid_status reads mddev->private, casts it to struct r5conf and

reads the entry max_nr_stripes.

However, if we have different raid type than 4/5/6, mddev->private

doesn't point to struct r5conf; it may point to struct r0conf, struct

r1conf, struct r10conf or struct mpconf. If we cast a pointer to one

of these structs to struct r5conf, we will be reading invalid memory

and KASAN warns about it.

Fix this bug by reading struct r5conf only if raid type is 4, 5 or 6.