CVE-2025-39717

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

open_tree_attr: do not allow id-mapping changes without OPEN_TREE_CLONE

As described in commit 7a54947e727b (Merge patch series fs: allow changing idmappings), open_tree_attr(2) was necessary in order to allow for a detached mount to be created and have its idmappings changed without the risk of any racing threads operating on it. For this reason, mount_setattr(2) still does not allow for id-mappings to be changed.

However, there was a bug in commit 2462651ffa76 (fs: allow changing idmappings) which allowed users to bypass this restriction by calling open_tree_attr(2) without OPEN_TREE_CLONE.

can_idmap_mount() prevented this bug from allowing an attached mountpoints id-mapping from being modified (thanks to an is_anon_ns() check), but this still allows for detached (but visible) mounts to have their be id-mapping changed. This risks the same UAF and locking issues as described in the merge commit, and was likely unintentional.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/69dbdc711d9130136824e3830191a6afffa0a1f0
• https://git.kernel.org/stable/c/9308366f062129d52e0ee3f7a019f7dd41db33df