Re: [PATCH v2 05/20] fscrypt: add extent-based encryption

Josef Bacik
2022-09-08T15:33:33Z

On Mon, Sep 05, 2022 at 08:35:20PM -0400, Sweet Tea Dorminy wrote:
> Some filesystems need to encrypt data based on extents, rather than on
> inodes, due to features incompatible with inode-based encryption. For
> instance, btrfs can have multiple inodes referencing a single block of
> data, and moves logical data blocks to different physical locations on
> disk in the background; these two features mean inode or
> physical-location-based policies will not work for btrfs.
>
> This change introduces fscrypt_extent_context objects, in analogy to
> existing context objects based on inodes. For a filesystem which uses
> extents, a new hook provides a new fscrypt_extent_context. During file
> content encryption/decryption, the existing fscrypt_context object
> provides key information, while the new fscrypt_extent_context provides
> IV information. For filename encryption, the existing IV generation
> methods are still used, since filenames are not stored in extents.
>
> As individually keyed inodes prevent sharing of extents, such policies
> are forbidden for filesystems with extent-based encryption.
>
> Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
> ---
> fs/crypto/crypto.c | 15 +++++++-
> fs/crypto/fscrypt_private.h | 26 ++++++++++++-
> fs/crypto/inline_crypt.c | 29 +++++++++++---
> fs/crypto/policy.c | 77 +++++++++++++++++++++++++++++++++++++
> include/linux/fscrypt.h | 41 ++++++++++++++++++++
> 5 files changed, 178 insertions(+), 10 deletions(-)
>
> diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
> index 7fe5979fbea2..77537736096b 100644
> --- a/fs/crypto/crypto.c
> +++ b/fs/crypto/crypto.c
> @@ -81,8 +81,19 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
> const struct fscrypt_info *ci)
> {
> u8 flags = fscrypt_policy_flags(&ci->ci_policy);
> + struct inode *inode = ci->ci_inode;
> + const struct fscrypt_operations *s_cop = inode->i_sb->s_cop;
>
> memset(iv, 0, ci->ci_mode->ivsize);
> + if (s_cop->get_extent_context && lblk_num != U64_MAX) {
> + size_t extent_offset;
> + union fscrypt_extent_context ctx;
> + int ret = fscrypt_get_extent_context(inode, lblk_num, &ctx, &extent_offset, NULL);

Newline between declarations and code, and since you use the warnon i'd do

int ret;

ret = fscrypt_get_extent_context();
WARN_ON_ONCE(ret);

> + WARN_ON_ONCE(ret != 0);
> + memcpy(iv->raw, ctx.v1.iv, ci->ci_mode->ivsize);
> + iv->lblk_num = iv->lblk_num + cpu_to_le64(extent_offset);
> + return;
> + }
>
> /*
> * Filename encryption. For inode-based policies, filenames are
> @@ -93,8 +104,8 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
>
> if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
> WARN_ON_ONCE(lblk_num > U32_MAX);
> - WARN_ON_ONCE(ci->ci_inode->i_ino > U32_MAX);
> - lblk_num |= (u64)ci->ci_inode->i_ino << 32;
> + WARN_ON_ONCE(inode->i_ino > U32_MAX);
> + lblk_num |= (u64)inode->i_ino << 32;
> } else if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
> WARN_ON_ONCE(lblk_num > U32_MAX);
> lblk_num = (u32)(ci->ci_hashed_ino + lblk_num);
> diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
> index 3afdaa084773..2092ef63c80a 100644
> --- a/fs/crypto/fscrypt_private.h
> +++ b/fs/crypto/fscrypt_private.h
> @@ -165,6 +165,27 @@ fscrypt_policy_flags(const union fscrypt_policy *policy)
> BUG();
> }
>
> +#define FSCRYPT_MAX_IV_SIZE 32
> +
> +/*
> + * fscrypt_extent_context - the encryption context for an extent
> + *

Whitespace.

> + * For filesystems that support extent encryption, this context provides the
> + * necessary randomly-initialized IV in order to encrypt/decrypt the data
> + * stored in the extent. It is stored alongside each extent, and is
> + * insufficient to decrypt the extent: the extent's owning inode(s) provide the
> + * policy information (including key identifier) necessary to decrypt.
> + */
> +struct fscrypt_extent_context_v1 {
> + u8 version;
> + u8 iv[FSCRYPT_MAX_IV_SIZE];
> +};
> +
> +union fscrypt_extent_context {
> + u8 version;
> + struct fscrypt_extent_context_v1 v1;
> +};
> +
> /*
> * For encrypted symlinks, the ciphertext length is stored at the beginning
> * of the string in little-endian format.
> @@ -279,8 +300,6 @@ fscrypt_msg(const struct inode *inode, const char *level, const char *fmt, ...);
> #define fscrypt_err(inode, fmt, ...) \
> fscrypt_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
>
> -#define FSCRYPT_MAX_IV_SIZE 32
> -
> union fscrypt_iv {
> struct {
> /* logical block number within the file */
> @@ -628,5 +647,8 @@ int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
> const union fscrypt_context *ctx_u,
> int ctx_size);
> const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir);
> +int fscrypt_get_extent_context(const struct inode *inode, u64 lblk_num,
> + union fscrypt_extent_context *ctx,
> + size_t *extent_offset, size_t *extent_length);
>
> #endif /* _FSCRYPT_PRIVATE_H */
> diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
> index 90f3e68f166e..0537f710047e 100644
> --- a/fs/crypto/inline_crypt.c
> +++ b/fs/crypto/inline_crypt.c
> @@ -1,3 +1,4 @@
> +

Whitespace. Thanks,

Josef