---
id: CVE-2026-98547
title: 'af_packet: fix integer overflow in prb_calc_retire_blk_tmo()'
summary: |-
  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) / (1…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    02afd75649a4e001031ed82153a5c39312ec0737
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    eb5b3838b9200dac04bfe33483db0ee8287456fb
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    297acc571d5813db76b147c745b91031d5f9c960
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    be1aacff399d519cc48d6b34354a54dd79041140
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    b2bcc6a254d6f27823a56787668ae4ee8cdb6e71
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    6279211e7d2456ecd195d236c9ee5e5c6fa5a17a
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    218a944b9e035d4b47d59c69af6ca13319da15fb
  - >-
    Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a <
    56d82862a0a243ac14ba11b6d7b57ddc2d064b95
  - Linux 3.2
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:18:15.669Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98547'
references:
  - url: 'https://git.kernel.org/stable/c/02afd75649a4e001031ed82153a5c39312ec0737'
  - url: 'https://git.kernel.org/stable/c/eb5b3838b9200dac04bfe33483db0ee8287456fb'
  - url: 'https://git.kernel.org/stable/c/297acc571d5813db76b147c745b91031d5f9c960'
  - url: 'https://git.kernel.org/stable/c/be1aacff399d519cc48d6b34354a54dd79041140'
  - url: 'https://git.kernel.org/stable/c/b2bcc6a254d6f27823a56787668ae4ee8cdb6e71'
  - url: 'https://git.kernel.org/stable/c/6279211e7d2456ecd195d236c9ee5e5c6fa5a17a'
  - url: 'https://git.kernel.org/stable/c/218a944b9e035d4b47d59c69af6ca13319da15fb'
  - url: 'https://git.kernel.org/stable/c/56d82862a0a243ac14ba11b6d7b57ddc2d064b95'
tags:
  - cve.org
ingestedAt: '2026-10-18T15:45:12.266Z'
---

## Overview

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.

## Affected

- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < 02afd75649a4e001031ed82153a5c39312ec0737`
- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < eb5b3838b9200dac04bfe33483db0ee8287456fb`
- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < 297acc571d5813db76b147c745b91031d5f9c960`
- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < be1aacff399d519cc48d6b34354a54dd79041140`
- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < b2bcc6a254d6f27823a56787668ae4ee8cdb6e71`
- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < 6279211e7d2456ecd195d236c9ee5e5c6fa5a17a`
- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < 218a944b9e035d4b47d59c69af6ca13319da15fb`
- `Linux >= f6fb8f100b807378fda19e83e5ac6828b638603a < 56d82862a0a243ac14ba11b6d7b57ddc2d064b95`
- `Linux 3.2`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.