CVE-2026-80806 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
ext4: don't enable DAX on new encrypted files
Currently, when a new encrypted regular file is created, the call to ext4_set_inode_flags(inode, init=true) in __ext4_new_inode() is made before EXT4_INODE_ENCRYPT is set. As a result, it can set S_DAX if the filesystem is mounted with "-o dax=always".
EXT4_INODE_ENCRYPT then actually gets set a bit later in __ext4_new_inode(), when it calls fscrypt_set_context() which calls ext4_set_context(). ext4_set_context() sets EXT4_INODE_ENCRYPT and calls ext4_set_inode_flags(inode, init=false) to set S_ENCRYPTED too.
This was intended to clear S_DAX as well. However, this was broken by commit 043546e46dc7 ("fs/ext4: Only change S_DAX on inode load"). This causes data written to the file to bypass encryption, also causing xfstests failures such as generic/548 (when "-o dax=always" is used).
Fix this by simplifying the flow by making __ext4_new_inode() set EXT4_INODE_ENCRYPT earlier. This makes it take effect in ext4_set_inode_flags(inode, init=true), making S_DAX never be set.
Similarly, make EXT4_STATE_MAY_INLINE_DATA never be set in the first place on new encrypted inodes. Then it doesn't need to be cleared.
As a result of these simplifications, ext4_set_context() no longer needs to change inode flags or state when 'handle != NULL'. Remove that too.
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel's ext4 filesystem driver contains a critical logic flaw in the initialization sequence for newly created encrypted regular files, specifically regarding the interaction between Direct Access (DAX) support and file encryption mechanisms. When a new encrypted file is instantiated via __ext4_new_inode(), the function initially calls ext4_set_inode_flags with an init flag set to true before the EXT4_INODE_ENCRYPT state bit is actually assigned to the inode structure. This ordering error creates a race condition where, if the filesystem has been mounted with the dax=always option, the kernel incorrectly sets the S_DAX flag on the new file's inode metadata. The intention of the original code was for subsequent operations to clear this DAX flag once encryption context is established, but due to a prior refactoring commit that restricted when S_DAX changes are applied during inode load, this clearing mechanism fails to execute correctly at the critical moment of creation.
This vulnerability results in data written to these newly created encrypted files bypassing the intended cryptographic protections provided by fscrypt. Because the DAX flag remains active on an inode marked for encryption but not yet fully processed by the encryption subsystem during its initial write operations, the kernel may map physical pages directly into user space without applying the necessary encryption transformations. This constitutes a severe confidentiality breach as sensitive data is stored in plaintext on disk despite administrative expectations of end-to-end encryption. The issue also leads to functional regressions evidenced by failures in standard filesystem test suites such as generic/548 when DAX is enabled, indicating that the file system behavior deviates from expected standards for encrypted storage operations.
From a classification perspective, this flaw aligns with CWE-20 Improper Input Validation and CWE-367 Time-of-check to Time-of-use (TOCTOU) race conditions, as the security state of the inode is checked or set in an incorrect temporal sequence relative to its operational configuration. In terms of adversarial tactics, this vulnerability facilitates data exfiltration through storage layer bypass techniques, mapping loosely to ATT&CK T1560 Archive Collected Data if attackers leverage DAX for rapid extraction, though primarily it represents a failure in access control enforcement (CWE-284) where encryption controls are not properly applied due to initialization sequence errors. The root cause lies in the dependency chain within __ext4_new_inode() where flag setting precedes state assignment, allowing privileged or local users with write permissions to create files that appear encrypted but operate without it under specific mount configurations.
The resolution involves restructuring the inode initialization logic to ensure EXT4_INODE_ENCRYPT is set earlier in the creation process so that ext4_set_inode_flags correctly identifies the encryption requirement and prevents S_DAX from being enabled during setup. Additionally, the fix ensures that EXT4_STATE_MAY_INLINE_DATA is never assigned to new encrypted inodes, removing unnecessary state management overhead. By correcting this initialization order, the kernel guarantees that DAX features are disabled for any file requiring fscrypt protection, thereby restoring data confidentiality and integrity. System administrators should ensure their kernels are updated with patches addressing this ext4 encryption sequence error and verify that dax=always mounts do not inadvertently expose encrypted volumes to plaintext storage risks.