CVE-2025-68736

Description

In the Linux kernel, the following vulnerability has been resolved:landlock: Fix handling of disconnected directoriesDisconnected files or directories can appear when they are visible andopened from a bind mount, but have been renamed or moved from the sourceof the bind mount in a way that makes them inaccessible from the mountpoint (i.e. out of scope).Previously, access rights tied to files or directories opened through adisconnected directory were collected by walking the related hierarchydown to the root of the filesystem, without taking into account themount point because it couldnt be found. This could lead toinconsistent access results, potential access right widening, andhard-to-debug renames, especially since such paths cannot be printed.For a sandboxed task to create a disconnected directory, it needs tohave write access (i.e. FS_MAKE_REG, FS_REMOVE_FILE, and FS_REFER) tothe underlying source of the bind mount, and read access to the relatedmount point. Because a sandboxed task cannot acquire more accessrights than those defined by its Landlock domain, this could lead toinconsistent access rights due to missing permissions that should beinherited from the mount point hierarchy, while inheriting permissionsfrom the filesystem hierarchy hidden by this mount point instead.Landlock now handles files and directories opened from disconnecteddirectories by taking into account the filesystem hierarchy when themount point is not found in the hierarchy walk, and also always takinginto account the mount point from which these disconnected directorieswere opened. This ensures that a rename is not allowed if it wouldwiden access rights [1].The rationale is that, even if disconnected hierarchies might not bevisible or accessible to a sandboxed task, relying on the collectedaccess rights from them improves the guarantee that access rights willnot be widened during a rename because of the access right comparisonbetween the source and the destination (see LANDLOCK_ACCESS_FS_REFER).It may look like this would grant more access on disconnected files anddirectories, but the security policies are always enforced for all theevaluated hierarchies. This new behavior should be less surprising tousers and safer from an access control perspective.Remove a wrong WARN_ON_ONCE() canary in collect_domain_accesses() andfix the related comment.Because opened files have their access rights stored in the related filesecurity properties, there is no impact for disconnected or unlinkedfiles.

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234