[v5.15] UBSAN: array-index-out-of-bounds in super_90_sync

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0248c33e835e Linux 5.15.221
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10cd67f9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=21845b39f8fc6be8
dashboard link: https://syzkaller.appspot.com/bug?extid=000832e490d9cdf268d8
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cdcbd8738a16/disk-0248c33e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/864175e96c3d/vmlinux-0248c33e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cb031d3f4011/bzImage-0248c33e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+000832...@syzkaller.appspotmail.com

md: error, md_import_device() returned -16
md/raid1:md0: active with 1 out of 124 mirrors
================================================================================
UBSAN: array-index-out-of-bounds in drivers/md/md.c:1556:20
index 28 is out of range for type 'mdp_disk_t[27]' (aka 'struct mdp_device_descriptor_s[27]')
CPU: 1 PID: 8346 Comm: syz.8.805 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
ubsan_epilogue+0xa/0x30 lib/ubsan.c:151
__ubsan_handle_out_of_bounds+0xdf/0xf0 lib/ubsan.c:282
super_90_sync+0x1371/0x22d0 drivers/md/md.c:1556
sync_super drivers/md/md.c:-1 [inline]
sync_sbs drivers/md/md.c:2681 [inline]
md_update_sb+0xf48/0x2380 drivers/md/md.c:2854
md_run+0x1a9d/0x2230 drivers/md/md.c:6114
do_md_run+0x30/0x400 drivers/md/md.c:6139
md_ioctl+0x2312/0x26f0 drivers/md/md.c:7793
blkdev_ioctl+0x347/0x6f0 block/ioctl.c:604
block_ioctl+0xac/0xf0 block/fops.c:496
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fea36305159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fea3455d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fea3658cfa0 RCX: 00007fea36305159
RDX: 0000000000000000 RSI: 00000000400c0930 RDI: 0000000000000006
RBP: 00007fea3639c06b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fea3658d038 R14: 00007fea3658cfa0 R15: 00007ffd39900888
</TASK>
================================================================================


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