The Linux kernel vulnerability CVE-2026-64156 concerns the netfs and AFS subsystems where write operations in directory and link writepages could be skipped improperly. Specifically, netfs_write_single() did not correctly handle cases where a write was skipped due to lock contention and WB_SYNC_NONE flags, failing to return the appropriate status and to re-mark the inode. The fix ensures netfs_write_single() returns 1 when a write is skipped and that afs_single_writepages() also skips accordingly, maintaining correct inode state. The vulnerability is mostly theoretical for directories because the affected code path is serialized by a validation lock, reducing practical risk.

If exploited, this vulnerability could cause skipped writes in directory or link writepages, potentially leading to inconsistent inode states in the virtual filesystem. However, the practical impact is limited and theoretical due to serialization in the code path, which reduces the chance of occurrence. There are no known exploits in the wild.

A fix has been implemented in the Linux kernel to address this issue by correcting the handling of skipped writes and inode marking in netfs_write_single() and afs_single_writepages(). Users should apply the official kernel updates that include this fix once available. Patch status is not yet confirmed in the provided data; check the vendor or Linux kernel advisories for the current remediation status.