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.
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/b5fa40226e71c17847b9ff2816c6ca4133d0d994
- https://git.kernel.org/stable/c/deff41898a5ae3a47db5fa1896a494aa95efda5d