# CVE-2022-49783: x86/fpu: Drop fpregs lock before inheriting FPU permissions

> A locking bug in the Linux kernel's x86 FPU code can cause a system crash when running with PREEMPT_RT enabled.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 May 2025
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2022-49783, GHSA-g5p7-q8gg-6qmf, ROOT-OS-UBUNTU-2204-CVE-2022-49783, UBUNTU-CVE-2022-49783

## What is CVE-2022-49783?

CVE-2022-49783 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 May 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

x86/fpu: Drop fpregs lock before inheriting FPU permissions

Mike Galbraith reported the following against an old fork of preempt-rt
but the same issue also applies to the current preempt-rt tree.

   BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
   in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd
   preempt_count: 1, expected: 0
   RCU nest depth: 0, expected: 0
   Preemption disabled at:
   fpu_clone
   CPU: 6 PID: 1 Comm: systemd Tainted: G            E       (unreleased)
   Call Trace:
    <TASK>
    dump_stack_lvl
    ? fpu_clone
    __might_resched
    rt_spin_lock
    fpu_clone
    ? copy_thread
    ? copy_process
    ? shmem_alloc_inode
    ? kmem_cache_alloc
    ? kernel_clone
    ? __do_sys_clone
    ? do_syscall_64
    ? __x64_sys_rt_sigprocmask
    ? syscall_exit_to_user_mode
    ? do_syscall_64
    ? syscall_exit_to_user_mode
    ? do_syscall_64
    ? syscall_exit_to_user_mode
    ? do_syscall_64
    ? exc_page_fault
    ? entry_SYSCALL_64_after_hwframe
    </TASK>

Mike says:

  The splat comes from fpu_inherit_perms() being called under fpregs_lock(),
  and us reaching the spin_lock_irq() therein due to fpu_state_size_dynamic()
  returning true despite static key __fpu_state_size_dynamic having never
  been enabled.

Mike's assessment looks correct. fpregs_lock on a PREEMPT_RT kernel disables
preemption so calling spin_lock_irq() in fpu_inherit_perms() is unsafe. This
problem exists since commit

  9e798e9aa14c ("x86/fpu: Prepare fpu_clone() for dynamically enabled features").

Even though the original bug report should not have enabled the paths at
all, the bug still exists.

fpregs_lock is necessary when editing the FPU registers or a task's FP
state but it is not necessary for fpu_inherit_perms(). The only write
of any FP state in fpu_inherit_perms() is for the new child which is
not running yet and cannot context switch or be borrowed by a kernel
thread yet. Hence, fpregs_lock is not protecting anything in the new
child until clone() completes and can be dropped earlier. The siglock
still needs to be acquired by fpu_inherit_perms() as the read of the
parent's permissions has to be serialised.

  [ bp: Cleanup splat. ]

## Which versions are affected by CVE-2022-49783?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2022-49783?

Apply the vendor's patch.

## Is CVE-2022-49783 being exploited?

There is no known exploitation of CVE-2022-49783 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2022-49783 and fix it if it is affected.

What it is: CVE-2022-49783 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 May 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2022-49783 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2022-49783/ (Markdown: https://insights.sbomify.com/CVE-2022-49783/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-49783
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-49783
- OSV: https://osv.dev/vulnerability/CVE-2022-49783

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-49783/
Summaries are generated and may contain mistakes; the official description above is the record.