CVE-2026-31649
type: TechArticle
description: In the Linux kernel, the following vulnerability has been resolved: net: stmmac: fix integer underflow in chain mode The jumbo_frm() chain-mode implementation unconditionally computes len = nopaged_len - bmax; where nopaged_len = skb_headlen(skb) (linear bytes only) and bmax is BUF_SIZE_8KiB or BUF_SIZE_2KiB. However, the caller stmmac_xmit() decides to invoke jumbo_frm() based on skb->len (total length including page fragments): is_jumbo = stmmac_is_jumbo_frm(priv, skb->len, enh_desc); When a packet has a small linear portion (nopaged_len <= bmax) but a large total length due to page fragments (skb->len > bmax), the subtraction wraps as an unsigned integer, producing a huge len value (~0xFFFFxxxx). This causes the while (len != 0) loop to execute hundreds of thousands of iterations, passing skb->data + bmax * i pointers far beyond the skb buffer to dma_map_single(). On IOMMU-less SoCs (the typical deployment for stmmac), this maps arbitrary kernel memory to the DMA en
date published: 2026-04-24T15:16:44.330
license: https://creativecommons.org/publicdomain/zero/1.0/
source: https://nvd.nist.gov/vuln/detail/CVE-2026-31649
publisher: AI Analytics
source organization: NIST National Vulnerability Database
main entity: Thing
  additional type: Vulnerability
  score: 9.8
  severity: CRITICAL
keywords: CWE-190

AI Analytics
type: Organization