---
id: CVE-2026-98299
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tcp: do not let tcp_rmem be set below 4096

  We can hit a division by zero crash in tcp_rcvbuf_grow()
  and tcp_rcv_space_adjust():

  divide error: 0000 [#1] PREEMPT SMP
  RI…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tcp: do not let tcp_rmem be set below 4096

  We can hit a division by zero crash in tcp_rcvbuf_grow()
  and tcp_rcv_space_adjust():

  divide error: 0000 [#1] PREEMPT SMP
  RI…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    879907631b9e70eedb62d76461b29afa106ebe7a
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    8e32532d0fa3191ecf9524b0e6bafa0832e712ba
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    67b83c15bed9eeeb8d1a6dbf88a5f79525970173
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    9a4f49bf8d2da4e52e904f60c29cca317bab9b3a
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    60df201dbb19a1bf6478b56d100f7ae1fe90e46a
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    7898bda1ebc198f5559b301a96dd5398edd4d4d3
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    1c4bb940c3bb4325bb88ac1b7eaf5faaa39e7d63
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    83a945a529d6e002dd7339c532288a931f463dba
  - Linux 2.6.12
published: '2026-10-06'
updated: '2026-10-06'
sourceUpdated: '2026-10-06T09:18:20.697'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98299'
references:
  - url: 'https://git.kernel.org/stable/c/1c4bb940c3bb4325bb88ac1b7eaf5faaa39e7d63'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/60df201dbb19a1bf6478b56d100f7ae1fe90e46a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/67b83c15bed9eeeb8d1a6dbf88a5f79525970173'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7898bda1ebc198f5559b301a96dd5398edd4d4d3'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/83a945a529d6e002dd7339c532288a931f463dba'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/879907631b9e70eedb62d76461b29afa106ebe7a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8e32532d0fa3191ecf9524b0e6bafa0832e712ba'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9a4f49bf8d2da4e52e904f60c29cca317bab9b3a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-06T08:50:17.414Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

tcp: do not let tcp_rmem be set below 4096

We can hit a division by zero crash in tcp_rcvbuf_grow()
and tcp_rcv_space_adjust():

divide error: 0000 [#1] PREEMPT SMP
RIP: 0010:tcp_rcvbuf_grow+0x187/0x450 net/ipv4/tcp_input.c:939
...
grow = div_u64(((u64)rcvwin << 1) * (newval - oldval), oldval);

The division uses oldval = tp->rcvq_space.space as divisor.
When tp->rcvq_space.space is zero, this leads to a divide-by-zero
exception.

tp->rcvq_space.space is initialized in tcp_init_buffer_space():
    tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
                                (u32)TCP_INIT_CWND * tp->advmss);

If tcp_rmem[1] is configured to very small values (such as 1),
sk->sk_rcvbuf is initialized to 1. Then tcp_full_space(sk), which
computes (sk->sk_rcvbuf * scaling_ratio) >> 8, truncates to 0.
This sets tp->window_clamp = 0, tp->rcv_ssthresh = 0, and
tp->rcvq_space.space = 0. Later, when data arrives and DRS is invoked,
tcp_rcvbuf_grow() divides by oldval == 0.

Back in 2015, commit b1cb59cf2efe ("net: sysctl_net_core: check SNDBUF
and RCVBUF for min length") ensured that net.core.rmem_default and
net.core.rmem_max cannot be set below SOCK_MIN_RCVBUF. Similarly,
SO_RCVBUF setsockopt enforces max_t(int, val * 2, SOCK_MIN_RCVBUF).

However, net.ipv4.tcp_rmem still had .extra1 = SYSCTL_ONE, allowing
arbitrarily small values.

Because SOCK_MIN_RCVBUF depends on sizeof(struct sk_buff) and cacheline
alignment, its value varies across architectures and configuration options.
Using a fixed constant of 4096 ensures a predictable, architecture-
independent lower bound that is safely above SOCK_MIN_RCVBUF everywhere
and matches the documented 4K default.

Fix this by setting tcp_rmem.extra1 to 4096 and updating the documentation.

## Remediation

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