# CVE-2026-98821: block: reject polled dio with user integrity metadata

> A local attacker can trigger a kernel crash via null pointer dereference in the block layer when using polled direct I/O with integrity metadata.

- **Severity:** Not scored
- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-98821, DEBIAN-CVE-2026-98821, GHSA-4mqf-mrhr-h3rh, UBUNTU-CVE-2026-98821

## What is CVE-2026-98821?

CVE-2026-98821 is a vulnerability in Linux, published on 18 Oct 2026. 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:

block: reject polled dio with user integrity metadata

IOCB_HAS_METADATA leaves iocb->private as a uio_meta, while
iocb_bio_iopoll() expects a bio. Since 2729a60bbfb9, metadata I/O
always uses __blkdev_direct_IO(), which never publishes the bio for
polling, so IOPOLL calls bio_poll() on the uio_meta.

Reproducer: io_uring IOPOLL plus a PI attribute on an integrity device
(scsi_debug dif=1 dix=1). KASAN reports:

  Oops: general protection fault, probably for non-canonical
  address 0xdffffc0000000004
  KASAN: null-ptr-deref in range
  [0x0000000000000020-0x0000000000000027]
  RIP: 0010:bio_poll+0x9d/0x4b0
  Call Trace:
   iocb_bio_iopoll+0x5b/0x80
   io_uring_classic_poll+0xf3/0x140
   io_do_iopoll+0x4e3/0xc00
   io_iopoll_check+0x275/0x560
   __do_sys_io_uring_enter+0x2e5/0x720

Return -EOPNOTSUPP when HIPRI is combined with user metadata.

## Which versions are affected by CVE-2026-98821?


## How do I fix CVE-2026-98821?

Apply the vendor's patch.

## Is CVE-2026-98821 being exploited?

There is no known exploitation of CVE-2026-98821 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98821 and fix it if it is affected.

What it is: CVE-2026-98821 is a vulnerability in Linux, published on 18 Oct 2026. 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-2026-98821 in the wild and no public exploit code.

Affected product: Linux. 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-2026-98821/ (Markdown: https://insights.sbomify.com/CVE-2026-98821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98821
- OSV: https://osv.dev/vulnerability/CVE-2026-98821

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98821/
Summaries are generated and may contain mistakes; the official description above is the record.