CVE-2026-89644

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix extent map leak in NOCOW direct I/O write

btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an

extent map reference that must be dropped on all exit paths.

For direct writes into a NOCOW range, btrfs_get_blocks_direct_write()

keeps using that extent map and asks btrfs_create_dio_extent() to

allocate the ordered extent. If that fails, for example because

btrfs_alloc_ordered_extent() fails, the function returns the error

without dropping the input extent map. The PREALLOC path avoided this by

dropping the input extent map before replacing it with the newly created

one.

Check the error from btrfs_create_dio_extent() before replacing the

map and drop the input extent map on failure.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References