fs: Add standard casefolding support

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 the use of utf8_casefold_hash to
avoid an allocation.

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>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/libfs.c b/fs/libfs.c
index e0d42e9..fc34361 100644 (file)
--- 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 +1365,88 @@ 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.
+ *
+ * Return: if names will need casefolding
+ */
+static bool needs_casefold(const struct inode *dir)
+{
+       return IS_CASEFOLDED(dir) && dir->i_sb->s_encoding;
+}
+
+/**
+ * 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 *dir = 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 (!dir || !needs_casefold(dir))
+               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 of the parent directory
+ * @str:       qstr of name whose hash we should fill in
+ *
+ * Return: 0 if hash was successful or unchanged, and -EINVAL on error
+ */
+int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)
+{
+       const struct inode *dir = READ_ONCE(dentry->d_inode);
+       struct super_block *sb = dentry->d_sb;
+       const struct unicode_map *um = sb->s_encoding;
+       int ret = 0;
+
+       if (!dir || !needs_casefold(dir))
+               return 0;
+
+       ret = utf8_casefold_hash(um, dentry, str);
+       if (ret < 0 && sb_has_strict_encoding(sb))
+               return -EINVAL;
+       return 0;
+}
+EXPORT_SYMBOL(generic_ci_d_hash);
+#endif

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7519ae0..bc5417c 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1371,6 +1371,12 @@ 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
  */
@@ -1441,6 +1447,10 @@ struct super_block {
 #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 */
        struct block_device     *s_bdev;
@@ -3262,6 +3272,12 @@ 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 *,