[RFC PATCH v11 03/51] fscrypt: export fscrypt_fname_encrypt and fscrypt_fname_encrypted_size

Jeff Layton
2022-03-22T14:13:48Z

For ceph, we want to use our own scheme for handling filenames that are
are longer than NAME_MAX after encryption and Base64 encoding. This
allows us to have a consistent view of the encrypted filenames for
clients that don't support fscrypt and clients that do but that don't
have the key.

Currently, fs/crypto only supports encrypting filenames using
fscrypt_setup_filename, but that also handles encoding nokey names. Ceph
can't use that because it handles nokey names in a different way.

Export fscrypt_fname_encrypt. Rename fscrypt_fname_encrypted_size to
__fscrypt_fname_encrypted_size and add a new wrapper called
fscrypt_fname_encrypted_size that takes an inode argument rather than a
pointer to a fscrypt_policy union.

Acked-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
fs/crypto/fname.c | 36 ++++++++++++++++++++++++++++++------
fs/crypto/fscrypt_private.h | 9 +++------
fs/crypto/hooks.c | 6 +++---
include/linux/fscrypt.h | 4 ++++
4 files changed, 40 insertions(+), 15 deletions(-)

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 1e4233c95005..77d38188a168 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -79,7 +79,8 @@ static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
/**
* fscrypt_fname_encrypt() - encrypt a filename
* @inode: inode of the parent directory (for regular filenames)
- * or of the symlink (for symlink targets)
+ * or of the symlink (for symlink targets). Key must already be
+ * set up.
* @iname: the filename to encrypt
* @out: (output) the encrypted filename
* @olen: size of the encrypted filename. It must be at least @iname->len.
@@ -130,6 +131,7 @@ int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,

return 0;
}
+EXPORT_SYMBOL_GPL(fscrypt_fname_encrypt);

/**
* fname_decrypt() - decrypt a filename
@@ -257,9 +259,9 @@ int fscrypt_base64url_decode(const char *src, int srclen, u8 *dst)
}
EXPORT_SYMBOL_GPL(fscrypt_base64url_decode);

-bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
- u32 orig_len, u32 max_len,
- u32 *encrypted_len_ret)
+bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
+ u32 orig_len, u32 max_len,
+ u32 *encrypted_len_ret)
{
int padding = 4 << (fscrypt_policy_flags(policy) &
FSCRYPT_POLICY_FLAGS_PAD_MASK);
@@ -273,6 +275,29 @@ bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
return true;
}

+/**
+ * fscrypt_fname_encrypted_size() - calculate length of encrypted filename
+ * @inode: parent inode of dentry name being encrypted. Key must
+ * already be set up.
+ * @orig_len: length of the original filename
+ * @max_len: maximum length to return
+ * @encrypted_len_ret: where calculated length should be returned (on success)
+ *
+ * Filenames that are shorter than the maximum length may have their lengths
+ * increased slightly by encryption, due to padding that is applied.
+ *
+ * Return: false if the orig_len is greater than max_len. Otherwise, true and
+ * fill out encrypted_len_ret with the length (up to max_len).
+ */
+bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
+ u32 max_len, u32 *encrypted_len_ret)
+{
+ return __fscrypt_fname_encrypted_size(&inode->i_crypt_info->ci_policy,
+ orig_len, max_len,
+ encrypted_len_ret);
+}
+EXPORT_SYMBOL_GPL(fscrypt_fname_encrypted_size);
+
/**
* fscrypt_fname_alloc_buffer() - allocate a buffer for presented filenames
* @max_encrypted_len: maximum length of encrypted filenames the buffer will be
@@ -428,8 +453,7 @@ int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
return ret;

if (fscrypt_has_encryption_key(dir)) {
- if (!fscrypt_fname_encrypted_size(&dir->i_crypt_info->ci_policy,
- iname->len, NAME_MAX,
+ if (!fscrypt_fname_encrypted_size(dir, iname->len, NAME_MAX,
&fname->crypto_buf.len))
return -ENAMETOOLONG;
fname->crypto_buf.name = kmalloc(fname->crypto_buf.len,
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index 5b0a9e6478b5..f3e6e566daff 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -297,14 +297,11 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
const struct fscrypt_info *ci);

/* fname.c */
-int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
- u8 *out, unsigned int olen);
-bool fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
- u32 orig_len, u32 max_len,
- u32 *encrypted_len_ret);
+bool __fscrypt_fname_encrypted_size(const union fscrypt_policy *policy,
+ u32 orig_len, u32 max_len,
+ u32 *encrypted_len_ret);

/* hkdf.c */
-
struct fscrypt_hkdf {
struct crypto_shash *hmac_tfm;
};
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index af74599ae1cf..7c01025879b3 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -228,9 +228,9 @@ int fscrypt_prepare_symlink(struct inode *dir, const char *target,
* counting it (even though it is meaningless for ciphertext) is simpler
* for now since filesystems will assume it is there and subtract it.
*/
- if (!fscrypt_fname_encrypted_size(policy, len,
- max_len - sizeof(struct fscrypt_symlink_data),
- &disk_link->len))
+ if (!__fscrypt_fname_encrypted_size(policy, len,
+ max_len - sizeof(struct fscrypt_symlink_data),
+ &disk_link->len))
return -ENAMETOOLONG;
disk_link->len += sizeof(struct fscrypt_symlink_data);

diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 671181d196a8..c90e176b5843 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -308,8 +308,12 @@ void fscrypt_free_inode(struct inode *inode);
int fscrypt_drop_inode(struct inode *inode);

/* fname.c */
+int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
+ u8 *out, unsigned int olen);
int fscrypt_base64url_encode(const u8 *src, int len, char *dst);
int fscrypt_base64url_decode(const char *src, int len, u8 *dst);
+bool fscrypt_fname_encrypted_size(const struct inode *inode, u32 orig_len,
+ u32 max_len, u32 *encrypted_len_ret);
int fscrypt_setup_filename(struct inode *inode, const struct qstr *iname,
int lookup, struct fscrypt_name *fname);

--
2.35.1