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.
It's 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 weren't
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 doesn't exist in the v2 policy equivalent
("per-mode keys"), since the data structures there are per super_block.
CSIRTS triage
- What
- Missing superblock check in find_or_insert_direct_key() allows improper key handling.
- Who is affected
- Systems using ext4, f2fs, or other filesystems with fscrypt encryption support.
- Urgency
- Medium priority; encryption key handling vulnerability requires patching.
- Action
- Apply Linux kernel security patches when available.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.09% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 1% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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