Bug 2424882 (CVE-2025-68368)

Summary: CVE-2025-68368 kernel: Kernel: Denial of Service in md driver via uninitialized bioset
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Multiple Device (md) driver. A local user can exploit this vulnerability by performing specific operations on `mdadm` (Multiple Device Administration) and `sysfs` (a virtual filesystem providing an interface to kernel data structures). This can lead to a NULL pointer dereference because the `bioset` is not properly initialized before I/O operations, resulting in a system crash and a Denial of Service (DoS).
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Description OSIDB Bzimport 2025-12-24 11:03:22 UTC 
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.
Comment 1 Alexander B 2025-12-25 15:37:18 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025122400-CVE-2025-68368-4e1b@gregkh/T