---
id: "CVE-2026-98821"
kind: "vulnerability"
aliases: ["CVE-2026-98821"]
title: "Linux kernel: polled direct I/O with user metadata crashes the block layer"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["block-devices", "io-uring", "linux-kernel", "runtime"]
not_affected_if: ["no-integrity-devices"]
published_at: "2026-10-18T16:17:36+00:00"
first_seen_at: "2026-10-23T21:57:17+00:00"
updated_at: "2026-10-25T05:14:42+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98821", "first_seen_at": "2026-10-23T21:57:17+00:00"}]
---

# Linux kernel: polled direct I/O with user metadata crashes the block layer

The Linux kernel block layer mishandles io_uring polled direct I/O when user integrity metadata is attached, dereferencing the wrong object and causing a kernel crash (KASAN null-pointer dereference in bio_poll). The sources describe a kernel oops reachable through io_uring IOPOLL on a protection-information device; they do not describe code execution or data disclosure.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- unknown

## Fix

- Apply the Linux kernel stable update that contains the upstream commit rejecting polled DIO with user integrity metadata (returns -EOPNOTSUPP on HIPRI with metadata); the sources do not name a version.

## Timeline

- 2026-10-23T21:57:17+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98821

## From the sources

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.

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