CVE-2026-89722
PCI/sysfs: Fix out-of-bounds read in pci_write_legacy_io()
Published Sep 11, 2026
CVSS 3.1 · 4.7 Medium
EPSS < 1%
KEV · Not listed
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.
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
-
CVE record
-
NVD configurations
No data
-
Red Hat packages
No data
-
OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
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No data.
No data.
| Vendor | Product | Versions | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux Kernel |
|
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| Linux | Linux Kernel |
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Remediation
Tracking
Advisories
| Source | ID | Title |
|---|---|---|
 Ubuntu USN |
USN-9019-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9020-1 | Linux kernel vulnerabilities |
Metrics
No CVSS v4.0
Attack Vector Local
Attack Complexity High
Privileges Required High
Scope Unchanged
Confidentiality Impact Low
Integrity Impact None
Availability Impact High
User Interaction None
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.206% probability within 30 days)
Key SSVC decision points have not yet been added.
References
History
Sep 12, 2026 12:15 AM
Weaknesses updated. Added references. Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-125 | |
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Sep 11, 2026 11:45 PM
Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | PCI/sysfs: Fix out-of-bounds read in pci_write_legacy_io() | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Subscriptions
Weaknesses
