In the Linux kernel, the following vulnerability has been resolved:
ext4: dont 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. Thats 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 the minimal fix for the above issue.)
Ive marked this as fixing the commit that introduced the call to fscrypt_limit_io_blocks(), since thats what made an actual crash start being possible. But this fix could be applied to any version of ext4 that supports the encrypt feature.