ext4: don't enable DAX on new encrypted files

Overview

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.

Affected

• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < add98959b220935b243170214c787bc03044a44d
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < f53b325068bca0b238c3e0d2eb7de9b1f2268cab
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < 5959cad3cfa852ec07bbdaf9c17f4838a94a8e6c
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < a13f61ba9b2a7a4ff1f140949ccfad23c5313757
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < ed1cd834da65db127f1c30ff67e78f14825a06c1
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < 458776af0061afec1014cb3cd0061e282e482e83
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < 3392391b363a63ebb531d45318a729b1c998565b
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < e27bae352158c007143d5bb50f3af33a177c0a37
• Linux >= 043546e46dc70c25ff7e2cf6d09cbb0424fc9978 < da32af420d6d466e247c43ac0b829edeac7ae0ad
• Linux 5.8

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.