CVE-2026-64600

Отчет

This flaw affects XFS filesystems that have the reflink feature enabled (reflink=1), which is the default configuration for XFS filesystems created on Red Hat Enterprise Linux 8 and later. The issue is a race condition where internal file mapping information becomes stale during a lock cycle but is not refreshed before being used to determine whether data blocks are shared between files. Exploitation requires local access and read permission to the target file. Systems using XFS without reflink enabled, or using other filesystems such as ext4, are not affected. Red Hat Enterprise Linux 7 and earlier are not affected, as the reflink feature is not available on those versions.

Меры по смягчению последствий

This vulnerability can be mitigated using a SystemTap script. To create and apply the mitigation, follow the steps below:

1. Install and configure SystemTap Install the SystemTap package and its dependencies following the instructions at: https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/10/html/monitoring_and_managing_system_status_and_performance/getting-started-with-systemtap
2. Create the mitigation script Create a file named refluxfs_mitigation.stp with the following contents:

3. Load the mitigation As the root user, execute SystemTap in guru mode:

Once the script is compiled and loaded, the following message will appear:

With the mitigation active, any application attempting to use reflink to copy files will receive -EOPNOTSUPP (-95) when calling the FICLONE ioctl (or its variants) or the copy_file_range() syscall. Important considerations:

1. SystemTap scripts are compiled into kernel modules. On systems with Secure Boot enabled, the kernel is in lockdown mode and will only load modules signed with a valid Secure Boot key or a key enrolled in the MOK. SystemTap can sign the generated module at compile time, but the user is responsible for key management. For instructions, refer to the "Sign a SystemTap module" section of: https://www.redhat.com/en/blog/secure-boot-systemtap
2. The SystemTap module is not persistent across reboots. If the machine is restarted or the stap process is terminated, the module will be unloaded and the mitigation must be reapplied.
3. Programs that rely on CoW/reflink without a fallback mechanism may fail, as reflink operations will be unavailable on any XFS filesystem while the mitigation is loaded. This includes the cp command when run with --reflink=always. In that case, use --reflink=auto instead, which is the default behavior in Red Hat Enterprise Linux.