CVE-2022-50277

/// Technical description

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

ext4: don't allow journal inode to have encrypt flag

Mounting a filesystem whose journal inode has the encrypt flag causes a

NULL dereference in fscrypt_limit_io_blocks() when the 'inlinecrypt'

mount option is used.

The problem is that when jbd2_journal_init_inode() calls bmap(), it

eventually finds its way into ext4_iomap_begin(), which calls

fscrypt_limit_io_blocks(). fscrypt_limit_io_blocks() requires that if

the inode is encrypted, then its encryption key must already be set up.

That's not the case here, since the journal inode is never "opened" like

a normal file would be. Hence the crash.

A reproducer is:

mkfs.ext4 -F /dev/vdb

debugfs -w /dev/vdb -R "set_inode_field <8> flags 0x80808"

mount /dev/vdb /mnt -o inlinecrypt

To fix this, make ext4 consider journal inodes with the encrypt flag to

be invalid. (Note, maybe other flags should be rejected on the journal

inode too. For now, this is just

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References