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From: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
To: "Theodore Y. Ts'o" <tytso@mit.edu>,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	Eric Biggers <ebiggers@kernel.org>, Chris Mason <clm@fb.com>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>,
	linux-fscrypt@vger.kernel.org, linux-btrfs@vger.kernel.org,
	kernel-team@meta.com
Cc: Omar Sandoval <osandov@osandov.com>,
	Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Subject: [PATCH v3 01/22] fscrypt: expose fscrypt_nokey_name
Date: Thu, 20 Oct 2022 12:58:20 -0400	[thread overview]
Message-ID: <4b42184921d1ab601505bd4c7075cf528a0933c9.1666281277.git.sweettea-kernel@dorminy.me> (raw)
In-Reply-To: <cover.1666281276.git.sweettea-kernel@dorminy.me>

From: Omar Sandoval <osandov@osandov.com>

btrfs stores its data structures, including filenames in directories, in
its own buffer implementation, struct extent_buffer, composed of
several non-contiguous pages. We could copy filenames into a
temporary buffer and use fscrypt_match_name() against that buffer, such
extensive memcpying would be expensive. Instead, exposing
fscrypt_nokey_name as in this change allows btrfs to recapitulate
fscrypt_match_name() using methods on struct extent_buffer instead of
dealing with a raw byte array.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/crypto/fname.c       | 39 +--------------------------------------
 include/linux/fscrypt.h | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 38 deletions(-)

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 12bd61d20f69..6c092a1533f7 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -14,7 +14,6 @@
 #include <linux/namei.h>
 #include <linux/scatterlist.h>
 #include <crypto/hash.h>
-#include <crypto/sha2.h>
 #include <crypto/skcipher.h>
 #include "fscrypt_private.h"
 
@@ -26,43 +25,7 @@
 #define FSCRYPT_FNAME_MIN_MSG_LEN 16
 
 /*
- * struct fscrypt_nokey_name - identifier for directory entry when key is absent
- *
- * When userspace lists an encrypted directory without access to the key, the
- * filesystem must present a unique "no-key name" for each filename that allows
- * it to find the directory entry again if requested.  Naively, that would just
- * mean using the ciphertext filenames.  However, since the ciphertext filenames
- * can contain illegal characters ('\0' and '/'), they must be encoded in some
- * way.  We use base64url.  But that can cause names to exceed NAME_MAX (255
- * bytes), so we also need to use a strong hash to abbreviate long names.
- *
- * The filesystem may also need another kind of hash, the "dirhash", to quickly
- * find the directory entry.  Since filesystems normally compute the dirhash
- * over the on-disk filename (i.e. the ciphertext), it's not computable from
- * no-key names that abbreviate the ciphertext using the strong hash to fit in
- * NAME_MAX.  It's also not computable if it's a keyed hash taken over the
- * plaintext (but it may still be available in the on-disk directory entry);
- * casefolded directories use this type of dirhash.  At least in these cases,
- * each no-key name must include the name's dirhash too.
- *
- * To meet all these requirements, we base64url-encode the following
- * variable-length structure.  It contains the dirhash, or 0's if the filesystem
- * didn't provide one; up to 149 bytes of the ciphertext name; and for
- * ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.
- *
- * This ensures that each no-key name contains everything needed to find the
- * directory entry again, contains only legal characters, doesn't exceed
- * NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only
- * take the performance hit of SHA-256 on very long filenames (which are rare).
- */
-struct fscrypt_nokey_name {
-	u32 dirhash[2];
-	u8 bytes[149];
-	u8 sha256[SHA256_DIGEST_SIZE];
-}; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */
-
-/*
- * Decoded size of max-size no-key name, i.e. a name that was abbreviated using
+ * Decoded size of max-size nokey name, i.e. a name that was abbreviated using
  * the strong hash and thus includes the 'sha256' field.  This isn't simply
  * sizeof(struct fscrypt_nokey_name), as the padding at the end isn't included.
  */
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index cad78b569c7e..4cdff7c15544 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -16,6 +16,7 @@
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
+#include <crypto/sha2.h>
 #include <uapi/linux/fscrypt.h>
 
 /*
@@ -54,6 +55,42 @@ struct fscrypt_name {
 #define fname_name(p)		((p)->disk_name.name)
 #define fname_len(p)		((p)->disk_name.len)
 
+/*
+ * struct fscrypt_nokey_name - identifier for directory entry when key is absent
+ *
+ * When userspace lists an encrypted directory without access to the key, the
+ * filesystem must present a unique "no-key name" for each filename that allows
+ * it to find the directory entry again if requested.  Naively, that would just
+ * mean using the ciphertext filenames.  However, since the ciphertext filenames
+ * can contain illegal characters ('\0' and '/'), they must be encoded in some
+ * way.  We use base64url.  But that can cause names to exceed NAME_MAX (255
+ * bytes), so we also need to use a strong hash to abbreviate long names.
+ *
+ * The filesystem may also need another kind of hash, the "dirhash", to quickly
+ * find the directory entry.  Since filesystems normally compute the dirhash
+ * over the on-disk filename (i.e. the ciphertext), it's not computable from
+ * no-key names that abbreviate the ciphertext using the strong hash to fit in
+ * NAME_MAX.  It's also not computable if it's a keyed hash taken over the
+ * plaintext (but it may still be available in the on-disk directory entry);
+ * casefolded directories use this type of dirhash.  At least in these cases,
+ * each no-key name must include the name's dirhash too.
+ *
+ * To meet all these requirements, we base64url-encode the following
+ * variable-length structure.  It contains the dirhash, or 0's if the filesystem
+ * didn't provide one; up to 149 bytes of the ciphertext name; and for
+ * ciphertexts longer than 149 bytes, also the SHA-256 of the remaining bytes.
+ *
+ * This ensures that each no-key name contains everything needed to find the
+ * directory entry again, contains only legal characters, doesn't exceed
+ * NAME_MAX, is unambiguous unless there's a SHA-256 collision, and that we only
+ * take the performance hit of SHA-256 on very long filenames (which are rare).
+ */
+struct fscrypt_nokey_name {
+	u32 dirhash[2];
+	u8 bytes[149];
+	u8 sha256[SHA256_DIGEST_SIZE];
+}; /* 189 bytes => 252 bytes base64url-encoded, which is <= NAME_MAX (255) */
+
 /* Maximum value for the third parameter of fscrypt_operations.set_context(). */
 #define FSCRYPT_SET_CONTEXT_MAX_SIZE	40
 
-- 
2.35.1


  reply	other threads:[~2022-10-20 16:59 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-20 16:58 [PATCH v3 00/22] btrfs: add fscrypt integration Sweet Tea Dorminy
2022-10-20 16:58 ` Sweet Tea Dorminy [this message]
2022-10-20 16:58 ` [PATCH v3 02/22] fscrypt: add fscrypt_have_same_policy() to check inode compatibility Sweet Tea Dorminy
2022-10-20 20:52   ` Josef Bacik
2022-10-20 16:58 ` [PATCH v3 03/22] fscrypt: allow fscrypt_generate_iv() to distinguish filenames Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 04/22] fscrypt: add extent-based encryption Sweet Tea Dorminy
2022-10-20 21:40   ` Eric Biggers
2022-10-20 22:20     ` Sweet Tea Dorminy
2022-10-20 21:45   ` Eric Biggers
2022-10-20 22:55     ` Sweet Tea Dorminy
2022-10-20 23:56       ` Eric Biggers
2022-10-21  0:37         ` Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 05/22] fscrypt: document btrfs' fscrypt quirks Sweet Tea Dorminy
2022-10-20 21:41   ` Eric Biggers
2022-10-20 22:07     ` Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 06/22] btrfs: use struct qstr instead of name and namelen Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 07/22] btrfs: setup qstrings from dentrys using fscrypt helper Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 08/22] btrfs: use struct fscrypt_str instead of struct qstr Sweet Tea Dorminy
2022-10-21 20:42   ` Josef Bacik
2022-10-20 16:58 ` [PATCH v3 09/22] btrfs: store directory encryption state Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 10/22] btrfs: disable various operations on encrypted inodes Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 11/22] btrfs: start using fscrypt hooks Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 12/22] btrfs: add fscrypt_context items Sweet Tea Dorminy
2022-10-21 20:54   ` Josef Bacik
2022-10-20 16:58 ` [PATCH v3 13/22] btrfs: translate btrfs encryption flags and encrypted inode flag Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 14/22] btrfs: store a fscrypt extent context per normal file extent Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 15/22] btrfs: encrypt normal file extent data if appropriate Sweet Tea Dorminy
2022-10-21 20:58   ` Josef Bacik
2022-10-20 16:58 ` [PATCH v3 16/22] btrfs: Add new FEATURE_INCOMPAT_ENCRYPT feature flag Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 17/22] btrfs: implement fscrypt ioctls Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 18/22] btrfs: permit searching for nokey names for removal Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 19/22] btrfs: use correct name hash for nokey names Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 20/22] btrfs: adapt lookup for partially encrypted directories Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 21/22] fscrypt: add flag allowing partially-encrypted directories Sweet Tea Dorminy
2022-10-20 16:58 ` [PATCH v3 22/22] btrfs: encrypt verity items Sweet Tea Dorminy
2022-10-20 21:38 ` [PATCH v3 00/22] btrfs: add fscrypt integration Eric Biggers
2022-10-20 23:12   ` David Sterba

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