Several file systems either have already implemented encryption or are in the process of doing so. This addresses usability and storage isolation requirements on mobile devices and in multi-tenant environments. While distinct keys locked down to user accounts protect the names and contents of individual files, a volume-level encryption key should protect the file system metadata. When using dm-crypt to do this, the blocks that the file system encrypts undergo another round of encryption. In many contexts this isn't necessary, and it results in decreased performance and increased power consumption. This discourages users and vendors from taking steps to protect file system metadata in addition to file contents. This patchset provides a new I/O request flag that suggests to lower layers that encryption may not be necessary because the file system has already done it. The first patch targets the block subsystem and adds the REQ_NOENCRYPT flag. The second patch targets dm-crypt and adds logic to observe the flag only when the user has opted-in by passing allow_encrypt_override as one of the optional parameters to the dm-crypt target. The third patch targets ext4 and sets the REQ_NOENCRYPT flag for blocks it encrypts and decrypts. The fourth patch does the same for f2fs. In this patchset I'm proposing that we make dm-crypt's observation of the file system "don't encrypt" request optional, but I'm not sure that's a good tradeoff. Under the assumption that encryption in upstream file systems is sound, the most common way I expect things can go awry is if the file system keys don't meet security requirements while dm-crypt keys do. However I'm not convinced that will end up being a widespread problem in practice, and there's a real data corruption concern with making dm-crypt's observation of the flag optional. The problem is that once dm-crypt observes the flag, it must always continue to do so or dm-crypt might decrypt content that it didn't encrypt. This can lead to scenarios where a vendor sets the dm-crypt option to observe the "don't encrypt" flag, and then down the road a user follows one of the many online guides to manually recover a dm-crypt partition without setting this new option. Should there be an encryption disable flag? I'm interested in considering other solutions. Michael Halcrow (4): block: Add bio req flag to disable encryption in block dm-crypt: Skip encryption of file system-encrypted blocks ext4: Set the bio REQ_NOENCRYPT flag f2fs: Set the bio REQ_NOENCRYPT flag drivers/md/dm-crypt.c | 17 +++++++++++++---- fs/crypto/bio.c | 2 +- fs/ext4/ext4.h | 3 +++ fs/ext4/inode.c | 13 ++++++++----- fs/ext4/page-io.c | 5 +++++ fs/ext4/readpage.c | 3 ++- fs/f2fs/data.c | 10 ++++++++-- include/linux/blk_types.h | 2 ++ 8 files changed, 42 insertions(+), 13 deletions(-) -- 2.13.1.508.gb3defc5cc-goog
