GHSA-CHVM-2QWM-X2XC
Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-11 21:31In the Linux kernel, the following vulnerability has been resolved:
PCI/sysfs: Fix out-of-bounds read in pci_write_legacy_io()
pci_write_legacy_io() loads 4 bytes from the kernfs write buffer regardless of how many bytes userspace wrote:
if (count != 1 && count != 2 && count != 4) return -EINVAL;
return pci_legacy_write(bus, off, (u32 )buf, count);
kernfs_fop_write_iter() allocates the buffer with kmalloc(len + 1), so a 1-byte write to the legacy_io sysfs file allocates 2 bytes and the unconditional u32 load reads up to 2 bytes past the end of the allocation, which KASAN reports as a slab-out-of-bounds read. Similarly, a 2-byte write overreads by 1 byte.
Thus, read only the number of bytes requested using get_unaligned_le16() and get_unaligned_le32() for the 2 and 4 byte cases, interpreting the buffer as little-endian to match the byte ordering of PCI I/O port space.
The PowerPC implementation previously compensated for the generic code's native-endian 32-bit load by shifting the value into place for the 1 and 2 byte cases. The shifts were only correct on big-endian kernels.
On little-endian PowerPC (POWER8 and later), they extracted the wrong bytes, so a 1-byte write wrote an out-of-bounds byte instead of the requested value. On big-endian, the native load also caused out_le16() and out_le32() to reverse the user's bytes on the wire for 2 and 4 byte writes. The little-endian helpers resolve both issues, so the shifts are removed.
No changes are needed for the Alpha platform.
The legacy_io file is root-only and exists only on Alpha and PowerPC, the two architectures that define HAVE_PCI_LEGACY.
{
"affected": [],
"aliases": [
"CVE-2026-89722"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-11T20:20:01Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nPCI/sysfs: Fix out-of-bounds read in pci_write_legacy_io()\n\npci_write_legacy_io() loads 4 bytes from the kernfs write buffer\nregardless of how many bytes userspace wrote:\n\n if (count != 1 \u0026\u0026 count != 2 \u0026\u0026 count != 4)\n return -EINVAL;\n\n return pci_legacy_write(bus, off, *(u32 *)buf, count);\n\nkernfs_fop_write_iter() allocates the buffer with kmalloc(len + 1),\nso a 1-byte write to the legacy_io sysfs file allocates 2 bytes and\nthe unconditional u32 load reads up to 2 bytes past the end of the\nallocation, which KASAN reports as a slab-out-of-bounds read.\nSimilarly, a 2-byte write overreads by 1 byte.\n\nThus, read only the number of bytes requested using get_unaligned_le16()\nand get_unaligned_le32() for the 2 and 4 byte cases, interpreting the\nbuffer as little-endian to match the byte ordering of PCI I/O port\nspace.\n\nThe PowerPC implementation previously compensated for the generic\ncode\u0027s native-endian 32-bit load by shifting the value into place\nfor the 1 and 2 byte cases. The shifts were only correct on\nbig-endian kernels.\n\nOn little-endian PowerPC (POWER8 and later), they extracted the wrong\nbytes, so a 1-byte write wrote an out-of-bounds byte instead of the\nrequested value. On big-endian, the native load also caused out_le16()\nand out_le32() to reverse the user\u0027s bytes on the wire for 2 and 4 byte\nwrites. The little-endian helpers resolve both issues, so the shifts\nare removed.\n\nNo changes are needed for the Alpha platform.\n\nThe legacy_io file is root-only and exists only on Alpha and PowerPC,\nthe two architectures that define HAVE_PCI_LEGACY.",
"id": "GHSA-chvm-2qwm-x2xc",
"modified": "2026-09-11T21:31:37Z",
"published": "2026-09-11T21:31:37Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89722"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7a99e9c7011905734cc2739038f2a224b6be0d1f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dc76258d0132df1d831a5a29758bd448ca9c566e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e892f05f1f790d5721cd8e3c561ed76da7e08bae"
}
],
"schema_version": "1.4.0",
"severity": []
}
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