# CVE-2022-48802: fs/proc: task_mmu.c: don't read mapcount for migration entry

> A race condition in the Linux kernel's proc filesystem allows a local attacker to trigger a kernel bug and cause a denial of service.

- **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:** 16 Jul 2024
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2022-48802, GHSA-m8cw-m65x-m5mc, UBUNTU-CVE-2022-48802

## What is CVE-2022-48802?

CVE-2022-48802 is a medium-severity vulnerability in Linux kernel, published on 16 Jul 2024. 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:

fs/proc: task_mmu.c: don't read mapcount for migration entry

The syzbot reported the below BUG:

  kernel BUG at include/linux/page-flags.h:785!
  invalid opcode: 0000 [#1] PREEMPT SMP KASAN
  CPU: 1 PID: 4392 Comm: syz-executor560 Not tainted 5.16.0-rc6-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
  RIP: 0010:PageDoubleMap include/linux/page-flags.h:785 [inline]
  RIP: 0010:__page_mapcount+0x2d2/0x350 mm/util.c:744
  Call Trace:
    page_mapcount include/linux/mm.h:837 [inline]
    smaps_account+0x470/0xb10 fs/proc/task_mmu.c:466
    smaps_pte_entry fs/proc/task_mmu.c:538 [inline]
    smaps_pte_range+0x611/0x1250 fs/proc/task_mmu.c:601
    walk_pmd_range mm/pagewalk.c:128 [inline]
    walk_pud_range mm/pagewalk.c:205 [inline]
    walk_p4d_range mm/pagewalk.c:240 [inline]
    walk_pgd_range mm/pagewalk.c:277 [inline]
    __walk_page_range+0xe23/0x1ea0 mm/pagewalk.c:379
    walk_page_vma+0x277/0x350 mm/pagewalk.c:530
    smap_gather_stats.part.0+0x148/0x260 fs/proc/task_mmu.c:768
    smap_gather_stats fs/proc/task_mmu.c:741 [inline]
    show_smap+0xc6/0x440 fs/proc/task_mmu.c:822
    seq_read_iter+0xbb0/0x1240 fs/seq_file.c:272
    seq_read+0x3e0/0x5b0 fs/seq_file.c:162
    vfs_read+0x1b5/0x600 fs/read_write.c:479
    ksys_read+0x12d/0x250 fs/read_write.c:619
    do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
    entry_SYSCALL_64_after_hwframe+0x44/0xae

The reproducer was trying to read /proc/$PID/smaps when calling
MADV_FREE at the mean time.  MADV_FREE may split THPs if it is called
for partial THP.  It may trigger the below race:

           CPU A                         CPU B
           -----                         -----
  smaps walk:                      MADV_FREE:
  page_mapcount()
    PageCompound()
                                   split_huge_page()
    page = compound_head(page)
    PageDoubleMap(page)

When calling PageDoubleMap() this page is not a tail page of THP anymore
so the BUG is triggered.

This could be fixed by elevated refcount of the page before calling
mapcount, but that would prevent it from counting migration entries, and
it seems overkilling because the race just could happen when PMD is
split so all PTE entries of tail pages are actually migration entries,
and smaps_account() does treat migration entries as mapcount == 1 as
Kirill pointed out.

Add a new parameter for smaps_account() to tell this entry is migration
entry then skip calling page_mapcount().  Don't skip getting mapcount
for device private entries since they do track references with mapcount.

Pagemap also has the similar issue although it was not reported.  Fixed
it as well.

[shy828301@gmail.com: v4]
[nathan@kernel.org: avoid unused variable warning in pagemap_pmd_range()]

## Which versions are affected by CVE-2022-48802?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2022-48802?

Apply the vendor's patch.

## Is CVE-2022-48802 being exploited?

There is no known exploitation of CVE-2022-48802 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-2022-48802 and fix it if it is affected.

What it is: CVE-2022-48802 is a medium-severity vulnerability in Linux kernel, published on 16 Jul 2024. 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-2022-48802 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-2022-48802/ (Markdown: https://insights.sbomify.com/CVE-2022-48802/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-48802
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-48802
- OSV: https://osv.dev/vulnerability/CVE-2022-48802

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-48802/
Summaries are generated and may contain mistakes; the official description above is the record.