# CVE-2026-98547: af_packet: fix integer overflow in prb_calc_retire_blk_tmo()

> A local attacker can trigger an integer overflow in the Linux kernel's af_packet module, causing a CPU spinlock and system denial of service.

- **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:** AZL-108659, BELL-CVE-2026-98547, DEBIAN-CVE-2026-98547, GHSA-9w5q-r82v-2r6x, UBUNTU-CVE-2026-98547

## What is CVE-2026-98547?

CVE-2026-98547 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:

af_packet: fix integer overflow in prb_calc_retire_blk_tmo()

prb_calc_retire_blk_tmo() computes in 32-bit int arithmetic:

        mbits = (blk_size_in_bytes * 8) / (1024 * 1024);

If I'm reading the validation right, tp_block_size is user
controlled and packet_set_ring() only rejects values that are <= 0
as int or not page aligned, so a 256MiB block goes right through
(and alloc_one_pg_vec_page() even has a vzalloc fallback for it).
0x10000000 * 8 wraps to INT_MIN, and on a NIC reporting 1 Gbps
(div == 1) the function ends up returning -2047.

The condition is actually (8 * size) mod 2^32 >= 2^31 && div == 1,
so the trigger set is [256,512), [768,1024), [1280,1536) and
[1792,2048) MiB. Other sizes wrap to non-negative values and faster
links divide the unsigned value back below 2^31, which is why this
doesn't blow up for everyone.

What makes it fatal is what happens next in init_prb_bdqc():

        p1->interval_ktime = ms_to_ktime(prb_calc_retire_blk_tmo(...));
        hrtimer_start(&p1->retire_blk_timer, p1->interval_ktime,
                      HRTIMER_MODE_REL_SOFT);

A negative relative timeout expires immediately. The callback
unconditionally returns HRTIMER_RESTART, and hrtimer_forward() turns
the negative interval into hrtimer_resolution:

        if (interval < hrtimer_resolution)
                interval = hrtimer_resolution;

So the SOFT timer re-fires at the maximum rate forever, holding
sk_receive_queue.lock each pass. One CPU spins in softirq until the
socket is closed. Repeat with more rings and the machine is gone.

The overflow itself is ancient - it was introduced together with
TPACKET_V3 in f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer
implementation."). Its effect prior to f7460d2989fa ("net:
af_packet: Use hrtimer to do the retire operation", v6.18) was not
as clear-cut, though: the return value was stored into an unsigned
short retire_blk_tov, so a negative result was truncated, and a
0-jiffy delay loop could be programmed as well. Neither is nearly
as detrimental as the immediate maximum-rate spin the hrtimer
conversion turned it into.

(Unrelated to CVE-2019-20812 - that one was the ethtool failure path
returning 0, which now returns DEFAULT_PRB_RETIRE_TOV.)

Reproducer, needs CAP_NET_RAW (a --network host container has it by
default) and a 1 Gbps NIC (QEMU e1000 works):

        int fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
        bind(fd, ...);
        int v = TPACKET_V3;
        setsockopt(fd, SOL_PACKET, PACKET_VERSION, &v, sizeof(v));
        struct tpacket_req3 req = {
                .tp_block_size = 0x10000000,
                .tp_block_nr = 1,
                .tp_frame_size = 2048,
                .tp_frame_nr = 0x10000000 / 2048,
                .tp_retire_blk_tov = 0,
        };
        setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &req, sizeof(req));

Compute in 64 bits instead. The operands are already bounded by the
existing validation, so nothing else changes. If you'd prefer a
different fix, just say so and I'll respin.

## Which versions are affected by CVE-2026-98547?


## How do I fix CVE-2026-98547?

Apply the vendor's patch.

## Is CVE-2026-98547 being exploited?

There is no known exploitation of CVE-2026-98547 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98547 and fix it if it is affected.

What it is: CVE-2026-98547 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-2026-98547 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-2026-98547/ (Markdown: https://insights.sbomify.com/CVE-2026-98547/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98547
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98547
- OSV: https://osv.dev/vulnerability/CVE-2026-98547

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98547/
Summaries are generated and may contain mistakes; the official description above is the record.