CVE-2026-68148

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

fscrypt: Add missing superblock check in find_or_insert_direct_key()

The legacy fscrypt_direct_keys table caches master keys that are used by v1 encryption policies that have FSCRYPT_POLICY_FLAG_DIRECT_KEY. Its just a global table for all filesystems (since the keys can be provided by the legacy process-subscribed keyrings mechanism, which makes it difficult to reuse super_block::s_master_keys).

The entries in it (struct fscrypt_direct_key) do contain a super_block pointer, though, for passing to fscrypt_destroy_inline_crypt_key() when the last inode that references the key is evicted.

However, when finding the fscrypt_direct_key for an inode, we werent actually comparing the super_block pointer. As a result, inodes with different super_blocks could point to the same fscrypt_direct_key. That could extend the lifetime of a fscrypt_direct_key beyond the super_block it points to, causing a use-after-free later.

Fix this by creating distinct fscrypt_direct_key structs for distinct super_block structs.

Note that this problem doesnt exist in the v2 policy equivalent (per-mode keys), since the data structures there are per super_block.

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 Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.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/330249609b70778094a7a36f5b6bcfa6362121d4
• https://git.kernel.org/stable/c/466f187b501a5ac8e1ea2ccf3ccd5c46108d8830
• https://git.kernel.org/stable/c/95376fe9c145be35566991df99c53134943d992f
• https://git.kernel.org/stable/c/965b5bc8cf5031225e057979ce660fec2bd5fbfc
• https://git.kernel.org/stable/c/b5fa40226e71c17847b9ff2816c6ca4133d0d994
• https://git.kernel.org/stable/c/deff41898a5ae3a47db5fa1896a494aa95efda5d