[PATCH v10 2/4] fs: Add standard casefolding support

Daniel Rosenberg
2020-07-07T11:45:33Z

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.

The new dentry operations are functionally equivalent to the existing
operations in ext4 and f2fs, apart from ths use of utf8_casefold_hash to
avoid an allocation, and dealing with casefolding and encryption. It
doesn't make sense to casefold the no-key token for the encrypted name,
so we don't casefold in that case.

By providing a common implementation, all users can benefit from any
optimizations without needing to port over improvements.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
---
fs/libfs.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 16 ++++++++
2 files changed, 112 insertions(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index 4d08edf19c78..f7df13806f36 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>

@@ -1363,3 +1365,97 @@ 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
+/*
+ * Determine if the name of a dentry should be casefolded. It does not make
+ * sense to casefold the no-key token of an encrypted filename.
+ *
+ * Return: if names will need casefolding
+ */
+static bool needs_casefold(const struct inode *dir, const struct dentry *dentry)
+{
+ return IS_CASEFOLDED(dir) && dir->i_sb->s_encoding &&
+ !(dentry->d_flags & DCACHE_ENCRYPTED_NAME);
+}
+
+/**
+ * generic_ci_d_compare - generic d_compare implementation for casefolding filesystems
+ * @dentry: dentry whose name we are checking against
+ * @len: len of name of dentry
+ * @str: str pointer to name of dentry
+ * @name: Name to compare against
+ *
+ * Return: 0 if names match, 1 if mismatch, or -ERRNO
+ */
+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;
+ struct qstr qstr = QSTR_INIT(str, len);
+ char strbuf[DNAME_INLINE_LEN];
+ int ret;
+
+ if (!inode || !needs_casefold(inode, dentry))
+ goto fallback;
+ /*
+ * If the dentry name is stored in-line, then it may be concurrently
+ * modified by a rename. If this happens, the VFS will eventually retry
+ * the lookup, so it doesn't matter what ->d_compare() returns.
+ * However, it's unsafe to call utf8_strncasecmp() with an unstable
+ * string. Therefore, we have to copy the name into a temporary buffer.
+ */
+ if (len <= DNAME_INLINE_LEN - 1) {
+ memcpy(strbuf, str, len);
+ strbuf[len] = 0;
+ qstr.name = strbuf;
+ /* prevent compiler from optimizing out the temporary buffer */
+ barrier();
+ }
+ ret = utf8_strncasecmp(um, name, &qstr);
+ if (ret >= 0)
+ return ret;
+
+ if (sb_has_strict_encoding(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 d_hash implementation for casefolding filesystems
+ * @dentry: dentry whose name we are hashing
+ * @str: qstr of name whose hash we should fill in
+ *
+ * Return: 0 if hash was successful, or -ERRNO
+ */
+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;
+ int ret = 0;
+
+ if (!inode || !needs_casefold(inode, dentry))
+ return 0;
+
+ ret = utf8_casefold_hash(um, dentry, str);
+ if (ret < 0)
+ goto err;
+
+ return 0;
+err:
+ if (sb_has_strict_encoding(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 3f881a892ea7..af8f2ecec8ff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1392,6 +1392,12 @@ 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 */
+#define SB_ENC_STRICT_MODE_FL (1 << 0)
+
+#define sb_has_strict_encoding(sb) \
+ (sb->s_encoding_flags & SB_ENC_STRICT_MODE_FL)
+
/*
* Umount options
*/
@@ -1461,6 +1467,10 @@ 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 */
@@ -3385,6 +3395,12 @@ 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);
+#endif
+
#ifdef CONFIG_MIGRATION
extern int buffer_migrate_page(struct address_space *,
struct page *, struct page *,
--
2.27.0.212.ge8ba1cc988-goog