# CVE-2021-47481: RDMA/mlx5: Initialize the ODP xarray when creating an ODP MR

> A missing initialization in the Linux kernel RDMA driver causes a null pointer dereference and system crash when deregistering memory regions.

- **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:** 22 May 2024
- **Updated:** 23 May 2026
- **Also known as:** DEBIAN-CVE-2021-47481, GHSA-7ghc-chxp-5r47, UBUNTU-CVE-2021-47481

## What is CVE-2021-47481?

CVE-2021-47481 is a medium-severity vulnerability in Linux kernel, published on 22 May 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:

RDMA/mlx5: Initialize the ODP xarray when creating an ODP MR

Normally the zero fill would hide the missing initialization, but an
errant set to desc_size in reg_create() causes a crash:

  BUG: unable to handle page fault for address: 0000000800000000
  PGD 0 P4D 0
  Oops: 0000 [#1] SMP PTI
  CPU: 5 PID: 890 Comm: ib_write_bw Not tainted 5.15.0-rc4+ #47
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
  RIP: 0010:mlx5_ib_dereg_mr+0x14/0x3b0 [mlx5_ib]
  Code: 48 63 cd 4c 89 f7 48 89 0c 24 e8 37 30 03 e1 48 8b 0c 24 eb a0 90 0f 1f 44 00 00 41 56 41 55 41 54 55 53 48 89 fb 48 83 ec 30 <48> 8b 2f 65 48 8b 04 25 28 00 00 00 48 89 44 24 28 31 c0 8b 87 c8
  RSP: 0018:ffff88811afa3a60 EFLAGS: 00010286
  RAX: 000000000000001c RBX: 0000000800000000 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000800000000
  RBP: 0000000800000000 R08: 0000000000000000 R09: c0000000fffff7ff
  R10: ffff88811afa38f8 R11: ffff88811afa38f0 R12: ffffffffa02c7ac0
  R13: 0000000000000000 R14: ffff88811afa3cd8 R15: ffff88810772fa00
  FS:  00007f47b9080740(0000) GS:ffff88852cd40000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000800000000 CR3: 000000010761e003 CR4: 0000000000370ea0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   mlx5_ib_free_odp_mr+0x95/0xc0 [mlx5_ib]
   mlx5_ib_dereg_mr+0x128/0x3b0 [mlx5_ib]
   ib_dereg_mr_user+0x45/0xb0 [ib_core]
   ? xas_load+0x8/0x80
   destroy_hw_idr_uobject+0x1a/0x50 [ib_uverbs]
   uverbs_destroy_uobject+0x2f/0x150 [ib_uverbs]
   uobj_destroy+0x3c/0x70 [ib_uverbs]
   ib_uverbs_cmd_verbs+0x467/0xb00 [ib_uverbs]
   ? uverbs_finalize_object+0x60/0x60 [ib_uverbs]
   ? ttwu_queue_wakelist+0xa9/0xe0
   ? pty_write+0x85/0x90
   ? file_tty_write.isra.33+0x214/0x330
   ? process_echoes+0x60/0x60
   ib_uverbs_ioctl+0xa7/0x110 [ib_uverbs]
   __x64_sys_ioctl+0x10d/0x8e0
   ? vfs_write+0x17f/0x260
   do_syscall_64+0x3c/0x80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

Add the missing xarray initialization and remove the desc_size set.

## Which versions are affected by CVE-2021-47481?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47481?

Apply the vendor's patch.

## Is CVE-2021-47481 being exploited?

There is no known exploitation of CVE-2021-47481 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-2021-47481 and fix it if it is affected.

What it is: CVE-2021-47481 is a medium-severity vulnerability in Linux kernel, published on 22 May 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-2021-47481 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-2021-47481/ (Markdown: https://insights.sbomify.com/CVE-2021-47481/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47481
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47481
- OSV: https://osv.dev/vulnerability/CVE-2021-47481

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47481/
Summaries are generated and may contain mistakes; the official description above is the record.