# CVE-2026-89722

## Summary

- **CVE ID:** CVE-2026-89722
- **Severity:** UNKNOWN
- **CVSS Score:** 0
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 16, 2026

## Description

In 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 Products

- Linux — Linux (1da177e4c3f41524e886b7f1b8a0c1fc7321cac2)
- Linux — Linux (0)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (2.6.12)

## References

- [CNA](https://git.kernel.org/stable/c/e892f05f1f790d5721cd8e3c561ed76da7e08bae)
- [CNA](https://git.kernel.org/stable/c/7a99e9c7011905734cc2739038f2a224b6be0d1f)
- [CNA](https://git.kernel.org/stable/c/dc76258d0132df1d831a5a29758bd448ca9c566e)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.20%
- **EPSS Percentile:** 9.8

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._