CVE-2025-68368

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

md: init bioset in mddev_init

IO operations may be needed before md_run(), such as updating metadata

after writing sysfs. Without bioset, this triggers a NULL pointer

dereference as below:

BUG: kernel NULL pointer dereference, address: 0000000000000020

Call Trace:

md_update_sb+0x658/0xe00

new_level_store+0xc5/0x120

md_attr_store+0xc9/0x1e0

sysfs_kf_write+0x6f/0xa0

kernfs_fop_write_iter+0x141/0x2a0

vfs_write+0x1fc/0x5a0

ksys_write+0x79/0x180

__x64_sys_write+0x1d/0x30

x64_sys_call+0x2818/0x2880

do_syscall_64+0xa9/0x580

entry_SYSCALL_64_after_hwframe+0x4b/0x53

Reproducer

```

mdadm -CR /dev/md0 -l1 -n2 /dev/sd[cd]

echo inactive > /sys/block/md0/md/array_state

echo 10 > /sys/block/md0/md/new_level

```

mddev_init() can only be called once per mddev, no need to test if bioset

has been initialized anymore.