CVE-2026-64294

/// Technical description

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

mm: do file ownership checks with the proper mount idmap

Ever since idmapped mounts were introduced, inode ownership checks (for

side-channel protection) in mincore() and madvise(MADV_PAGEOUT) were done

against the nop_mnt_idmap, which completely ignores the file's mount's

idmap. This results in odd edgecases like:

1) mount/bind-mount with an idmap userA:userB:1

2) userB runs an owner_or_capable() check on file that is owned by userA

on-disk/in-memory, but owned by userB after idmap translation

3) owner_or_capable() mysteriously fails as the correct idmap wasn't supplied

In the case of mincore/madvise MADV_PAGEOUT, this is usually benign,

because file_permission(file, MAY_WRITE) will probably succeed, as it uses

the proper idmap internally, but it does not need to be the case on e.g a

0444 file where even the owner itself doesn't have permissions to write to

it.

Since this is clearly not trivial to get right, int

/// 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