CVE-2026-31649 (GCVE-0-2026-31649)

Vulnerability from cvelistv5 – Published: 2026-04-24 14:45 – Updated: 2026-04-27 14:04
VLAI?
Title
net: stmmac: fix integer underflow in chain mode
Summary
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 engine, constituting a kernel memory disclosure and potential memory corruption from hardware. Fix this by introducing a buf_len local variable clamped to min(nopaged_len, bmax). Computing len = nopaged_len - buf_len is then always safe: it is zero when the linear portion fits within a single descriptor, causing the while (len != 0) loop to be skipped naturally, and the fragment loop in stmmac_xmit() handles page fragments afterward.
Severity ?
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < 513e06735f5be575b409d195822195348b164e48 (git)
Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < 275bdf762e82082f064e60a92448fa2ac43cf95b (git)
Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < a2b68a9a476b9544ff31f1fbcd5d80867a8a5e2f (git)
Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < b7b8012193fd98236d7ae05d4b553f010a77b2ef (git)
Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < 2c91b39912278d0878f9ba60ba04d2518b18a08d (git)
Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < 6fca757c20396dc2e604dcc61922264e9e3dc803 (git)
Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < 10d12b9240ebf96c785f0e2e4228318cd5f3a3eb (git)
Affected: 286a837217204b1ef105e3a554d0757e4fdfaac1 , < 51f4e090b9f87b40c21b6daadb5c06e6c0a07b67 (git)
Create a notification for this product.
    Linux Linux Affected: 3.2
Unaffected: 0 , < 3.2 (semver)
Unaffected: 5.10.253 , ≤ 5.10.* (semver)
Unaffected: 5.15.203 , ≤ 5.15.* (semver)
Unaffected: 6.1.169 , ≤ 6.1.* (semver)
Unaffected: 6.6.135 , ≤ 6.6.* (semver)
Unaffected: 6.12.82 , ≤ 6.12.* (semver)
Unaffected: 6.18.23 , ≤ 6.18.* (semver)
Unaffected: 6.19.13 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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However, the caller stmmac_xmit()\\ndecides to invoke jumbo_frm() based on skb-\u003elen (total length including\\npage fragments):\\n\\n    is_jumbo = stmmac_is_jumbo_frm(priv, skb-\u003elen, enh_desc);\\n\\nWhen a packet has a small linear portion (nopaged_len \u003c= bmax) but a\\nlarge total length due to page fragments (skb-\u003elen \u003e bmax), the\\nsubtraction wraps as an unsigned integer, producing a huge len value\\n(~0xFFFFxxxx).  This causes the while (len != 0) loop to execute\\nhundreds of thousands of iterations, passing skb-\u003edata + bmax * i\\npointers far beyond the skb buffer to dma_map_single().  On IOMMU-less\\nSoCs (the typical deployment for stmmac), this maps arbitrary kernel\\nmemory to the DMA engine, constituting a kernel memory disclosure and\\npotential memory corruption from hardware.\\n\\nFix this by introducing a buf_len local variable clamped to\\nmin(nopaged_len, bmax).  Computing len = nopaged_len - buf_len is then\\nalways safe: it is zero when the linear portion fits within a single\\ndescriptor, causing the while (len != 0) loop to be skipped naturally,\\nand the fragment loop in stmmac_xmit() handles page fragments 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  }
}


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