# CVE-2021-46947: sfc: adjust efx->xdp_tx_queue_count with the real number of initialized queues

> A null pointer dereference in the Linux kernel sfc driver allows local attackers to cause a system crash via ethtool commands.

- **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:** No
- **Published:** 27 Feb 2024
- **Updated:** 11 May 2026
- **Also known as:** GHSA-7jpg-53q7-h4w6, UBUNTU-CVE-2021-46947

## What is CVE-2021-46947?

CVE-2021-46947 is a medium-severity vulnerability in Linux kernel, published on 27 Feb 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:

sfc: adjust efx->xdp_tx_queue_count with the real number of initialized queues

efx->xdp_tx_queue_count is initially initialized to num_possible_cpus() and is
later used to allocate and traverse efx->xdp_tx_queues lookup array. However,
we may end up not initializing all the array slots with real queues during
probing. This results, for example, in a NULL pointer dereference, when running
"# ethtool -S <iface>", similar to below

[2570283.664955][T4126959] BUG: kernel NULL pointer dereference, address: 00000000000000f8
[2570283.681283][T4126959] #PF: supervisor read access in kernel mode
[2570283.695678][T4126959] #PF: error_code(0x0000) - not-present page
[2570283.710013][T4126959] PGD 0 P4D 0
[2570283.721649][T4126959] Oops: 0000 [#1] SMP PTI
[2570283.734108][T4126959] CPU: 23 PID: 4126959 Comm: ethtool Tainted: G           O      5.10.20-cloudflare-2021.3.1 #1
[2570283.752641][T4126959] Hardware name: <redacted>
[2570283.781408][T4126959] RIP: 0010:efx_ethtool_get_stats+0x2ca/0x330 [sfc]
[2570283.796073][T4126959] Code: 00 85 c0 74 39 48 8b 95 a8 0f 00 00 48 85 d2 74 2d 31 c0 eb 07 48 8b 95 a8 0f 00 00 48 63 c8 49 83 c4 08 83 c0 01 48 8b 14 ca <48> 8b 92 f8 00 00 00 49 89 54 24 f8 39 85 a0 0f 00 00 77 d7 48 8b
[2570283.831259][T4126959] RSP: 0018:ffffb79a77657ce8 EFLAGS: 00010202
[2570283.845121][T4126959] RAX: 0000000000000019 RBX: ffffb799cd0c9280 RCX: 0000000000000018
[2570283.860872][T4126959] RDX: 0000000000000000 RSI: ffff96dd970ce000 RDI: 0000000000000005
[2570283.876525][T4126959] RBP: ffff96dd86f0a000 R08: ffff96dd970ce480 R09: 000000000000005f
[2570283.892014][T4126959] R10: ffffb799cd0c9fff R11: ffffb799cd0c9000 R12: ffffb799cd0c94f8
[2570283.907406][T4126959] R13: ffffffffc11b1090 R14: ffff96dd970ce000 R15: ffffffffc11cd66c
[2570283.922705][T4126959] FS:  00007fa7723f8740(0000) GS:ffff96f51fac0000(0000) knlGS:0000000000000000
[2570283.938848][T4126959] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[2570283.952524][T4126959] CR2: 00000000000000f8 CR3: 0000001a73e6e006 CR4: 00000000007706e0
[2570283.967529][T4126959] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[2570283.982400][T4126959] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[2570283.997308][T4126959] PKRU: 55555554
[2570284.007649][T4126959] Call Trace:
[2570284.017598][T4126959]  dev_ethtool+0x1832/0x2830

Fix this by adjusting efx->xdp_tx_queue_count after probing to reflect the true
value of initialized slots in efx->xdp_tx_queues.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-46947?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-46947?

No fix has been published for CVE-2021-46947 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-46947 being exploited?

There is no known exploitation of CVE-2021-46947 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-2021-46947 and fix it if it is affected.

What it is: CVE-2021-46947 is a medium-severity vulnerability in Linux kernel, published on 27 Feb 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-2021-46947 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-2021-46947/ (Markdown: https://insights.sbomify.com/CVE-2021-46947/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-46947
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-46947
- OSV: https://osv.dev/vulnerability/CVE-2021-46947

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-46947/
Summaries are generated and may contain mistakes; the official description above is the record.