On Wed, Mar 25, 2020 at 08:07:00PM -0700, Satya Tangirala wrote:
> +/* Enable inline encryption for this file if supported. */
> +void fscrypt_select_encryption_impl(struct fscrypt_info *ci)
> +{
> + const struct inode *inode = ci->ci_inode;
> + struct super_block *sb = inode->i_sb;
> +
> + /* The file must need contents encryption, not filenames encryption */
> + if (!fscrypt_needs_contents_encryption(inode))
> + return;
> +
> + /* blk-crypto must implement the needed encryption algorithm */
> + if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
> + return;
> +
> + /* The filesystem must be mounted with -o inlinecrypt */
> + if (!(sb->s_flags & SB_INLINECRYPT))
> + return;
> +
> + ci->ci_inlinecrypt = true;
> +}
A bug I came across last week when writing a new test is that '-o inlinecrypt'
can break some fscrypt settings because it enables blk-crypto even when
CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK is unset and the hardware doesn't support
the algorithm. For example, adding '-o inlinecrypt' can make Adiantum-encrypted
files stop working, due to the hardware only supporting AES-XTS.
That's undesirable. Adding '-o inlinecrypt' should just make inline encryption
be used where it can, and not break anything.
To fix this, we should make fscrypt_select_encryption_impl() only set
->ci_inlinecrypt if either blk-crypto-fallback is enabled or if all the
filesystem's devices support the algorithm.
In v7+ of this patchset, this is a bit tricky because now
blk_ksm_crypto_key_supported() takes in a 'struct blk_crypto_key', which
fscrypt_select_encryption_impl() doesn't have available yet. Perhaps make
blk_ksm_crypto_key_supported() a wrapper around a function like
blk_ksm_crypto_setting_supported() that takes a new struct:
struct blk_crypto_setting {
enum blk_crypto_mode_num crypto_mode;
unsigned int data_unit_size;
unsigned int dun_bytes;
};
Then maybe add blk_crypto_setting_supported() which returns true if either
blk_ksm_crypto_key_supported() *or* blk-crypto-fallback is enabled.
- Eric
