[PATCH v8 2/8] fs: Add standard casefolding support

[Daniel Rosenberg <drosen@google.com>]

This adds general supporting functions for filesystems that use
utf8 casefolding. It provides standard dentry_operations and adds the
necessary structures in struct super_block to allow this standardization.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
---
 fs/libfs.c         | 114 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  22 +++++++++
 2 files changed, 136 insertions(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index c686bd9caac67..0eaa63a9ae037 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -20,6 +20,8 @@
 #include <linux/fs_context.h>
 #include <linux/pseudo_fs.h>
 #include <linux/fsnotify.h>
+#include <linux/unicode.h>
+#include <linux/fscrypt.h>
 
 #include <linux/uaccess.h>
 
@@ -1361,3 +1363,115 @@ bool is_empty_dir_inode(struct inode *inode)
 	return (inode->i_fop == &empty_dir_operations) &&
 		(inode->i_op == &empty_dir_inode_operations);
 }
+
+#ifdef CONFIG_UNICODE
+/**
+ * needs_casefold - determine if casefolding applies for a given directory
+ * @dir:	Folder to check
+ *
+ * This function returns true if dentries within this folder should be
+ * casefolded. If a folder is encrypted, but we don't have the key, it is not
+ * meaningful to casefold the no-key token name.
+ */
+bool needs_casefold(const struct inode *dir)
+{
+	return IS_CASEFOLDED(dir) && dir->i_sb->s_encoding &&
+			(!IS_ENCRYPTED(dir) || fscrypt_has_encryption_key(dir));
+}
+EXPORT_SYMBOL(needs_casefold);
+
+/*
+ * Under RCU, small names may change, but utf8 expects a stable name
+ * This operates similarly to take_dentry_name_snapshot, except that there
+ * is no guarantee that it grabs a coherent string.
+ */
+static int make_name_stable(const struct unicode_map *um,
+			   const struct dentry *dentry, struct qstr *entry,
+			   char *buff)
+{
+	if (dentry->d_iname != (const unsigned char *)entry->name)
+		return 0;
+
+	memcpy(buff, entry->name, entry->len + 1);
+	entry->name = buff;
+	return utf8_validate(um, entry);
+}
+
+/**
+ * generic_ci_d_compare - generic implementation of d_compare for casefolding
+ * @dentry: Entry we are comparing against
+ * @len: length of str
+ * @str: name of the dentry, safely paired with len
+ * @name: qstr to test against
+ *
+ * This performs a case insensitive comparison between the given name and str.
+ * It can be used as d_compare for dentry_operations.
+ */
+int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
+			  const char *str, const struct qstr *name)
+{
+	const struct dentry *parent = READ_ONCE(dentry->d_parent);
+	const struct inode *inode = READ_ONCE(parent->d_inode);
+	const struct super_block *sb = dentry->d_sb;
+	const struct unicode_map *um = sb->s_encoding;
+	char small_name[DNAME_INLINE_LEN];
+	struct qstr entry = QSTR_INIT(str, len);
+	int ret;
+
+	if (!inode || !needs_casefold(inode))
+		goto fallback;
+
+	/* Under RCU, small names may change, but utf8 expects a stable name */
+	if (make_name_stable(um, dentry, &entry, small_name))
+		goto err;
+	ret = utf8_strncasecmp(um, name, &entry);
+	if (ret >= 0)
+		return ret;
+err:
+	if (sb_has_enc_strict_mode(sb))
+		return -EINVAL;
+fallback:
+	if (len != name->len)
+		return 1;
+	return !!memcmp(str, name->name, len);
+}
+EXPORT_SYMBOL(generic_ci_d_compare);
+
+/**
+ * generic_ci_d_hash - generic implementation of d_hash for casefolding
+ * @dentry: Entry whose name we are hashing
+ * @len: length of str
+ * @qstr: name of the dentry, safely paired with len
+ * @str: qstr to set hash of
+ *
+ * This performs a case insensitive hash of the given str.
+ * If casefolding is not required, it leaves the hash unchanged.
+ */
+int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)
+{
+	const struct inode *inode = READ_ONCE(dentry->d_inode);
+	struct super_block *sb = dentry->d_sb;
+	const struct unicode_map *um = sb->s_encoding;
+	char small_name[DNAME_INLINE_LEN];
+	struct qstr entry = QSTR_INIT(str->name, str->len);
+	int ret = 0;
+
+	if (!inode || !needs_casefold(inode))
+		return 0;
+
+	if (make_name_stable(um, dentry, &entry, small_name))
+		goto err;
+	ret = utf8_casefold_hash(um, dentry, &entry);
+	if (ret < 0)
+		goto err;
+
+	return 0;
+err:
+	if (sb_has_enc_strict_mode(sb))
+		ret = -EINVAL;
+	else
+		ret = 0;
+	return ret;
+}
+EXPORT_SYMBOL(generic_ci_d_hash);
+#endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3cd4fe6b845e7..8d20a3daa49a0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1382,6 +1382,12 @@ extern int send_sigurg(struct fown_struct *fown);
 #define SB_ACTIVE	(1<<30)
 #define SB_NOUSER	(1<<31)
 
+/* These flags relate to encoding and casefolding, and are stored on disk */
+#define SB_ENC_STRICT_MODE_FL	(1 << 0)
+
+#define sb_has_enc_strict_mode(sb) \
+	(sb->s_encoding_flags & SB_ENC_STRICT_MODE_FL)
+
 /*
  *	Umount options
  */
@@ -1449,6 +1455,10 @@ struct super_block {
 #endif
 #ifdef CONFIG_FS_VERITY
 	const struct fsverity_operations *s_vop;
+#endif
+#ifdef CONFIG_UNICODE
+	struct unicode_map *s_encoding;
+	u16 s_encoding_flags;
 #endif
 	struct hlist_bl_head	s_roots;	/* alternate root dentries for NFS */
 	struct list_head	s_mounts;	/* list of mounts; _not_ for fs use */
@@ -3368,6 +3378,18 @@ extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
 
 extern int generic_check_addressable(unsigned, u64);
 
+#ifdef CONFIG_UNICODE
+extern int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str);
+extern int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
+				const char *str, const struct qstr *name);
+extern bool needs_casefold(const struct inode *dir);
+#else
+static inline bool needs_casefold(const struct inode *dir)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_MIGRATION
 extern int buffer_migrate_page(struct address_space *,
 				struct page *, struct page *,
-- 
2.25.1.481.gfbce0eb801-goog