diff mbox series

[03/36] fscrypt: export fscrypt_fname_encrypt and fscrypt_fname_encrypted_size

Message ID 20211209153647.58953-4-jlayton@kernel.org (mailing list archive)
State New, archived
Headers show
Series ceph+fscrypt: context, filename, symlink and size handling support | expand

Commit Message

Jeff Layton Dec. 9, 2021, 3:36 p.m. UTC 
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.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/crypto/fname.c           | 32 +++++++++++++++++++++++++++-----
 fs/crypto/fscrypt_private.h |  9 +++------
 fs/crypto/hooks.c           |  6 +++---
 include/linux/fscrypt.h     |  4 ++++
 4 files changed, 37 insertions(+), 14 deletions(-)

Comments

Eric Biggers Dec. 10, 2021, 7:32 p.m. UTC | #1 
On Thu, Dec 09, 2021 at 10:36:14AM -0500, Jeff Layton wrote:
> 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

base64 => Base64.  (base64 and base64url are types of Base64.)

> diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
> index 8fa23d525b5c..3be04b5aa570 100644
> --- a/fs/crypto/fname.c
> +++ b/fs/crypto/fname.c
> @@ -130,6 +130,7 @@ int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
>  
>  	return 0;
>  }
> +EXPORT_SYMBOL(fscrypt_fname_encrypt);

The documentation for the @inode parameter could use a mention that the inode's
key must have already been set up.  External callers could get that wrong.

Also, I'd prefer EXPORT_SYMBOL_GPL for anything that isn't generic functionality
like Base64 encoding/decoding.

> +/**
> + * fscrypt_fname_encrypted_size() - calculate length of encrypted filename
> + * @inode: 		parent inode of dentry name being encrypted

Likewise, this should mention that the inode's key must have already been set
up.

> + * Filenames must be padded out to at least the end of an fscrypt block before
> + * encrypting them.

That's not really correct.  The padding amount depends on the padding flags, as
well as whether the filename gets truncated at max_len or not.  Also there's not
really any such thing as an "fscrypt block".  (FS_CRYPTO_BLOCK_SIZE, which is 16
bytes, is misnamed.  It really should be two separate things like
FSCRYPT_MIN_FNAME_CTEXT_SIZE and FSCRYPT_CONTENTS_CTEXT_ALIGNMENT.)

How about just writing something like:

    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 shorter than max_len. Otherwise, true and
> + * 	   fill out encrypted_len_ret with the length (up to max_len).

false if orig_len is *greater* than max_len.

> diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
> index 5b0a9e6478b5..51e42767dbd6 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);

This is indented with spaces, not tabs.

- Eric
diff mbox series

Patch

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 8fa23d525b5c..3be04b5aa570 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -130,6 +130,7 @@  int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
 
 	return 0;
 }
+EXPORT_SYMBOL(fscrypt_fname_encrypt);
 
 /**
  * fname_decrypt() - decrypt a filename
@@ -257,9 +258,9 @@  int fscrypt_base64url_decode(const char *src, int srclen, u8 *dst)
 }
 EXPORT_SYMBOL(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 +274,28 @@  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
+ * @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 must be padded out to at least the end of an fscrypt block before
+ * encrypting them. This calculates the length of an encrypted filename.
+ *
+ * Return: false if the orig_len is shorter 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(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 +451,7 @@  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..51e42767dbd6 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);