libfs: Introduce case-insensitive string comparison helper

generic_ci_match can be used by case-insensitive filesystems to compare
strings under lookup with dirents in a case-insensitive way.  This
function is currently reimplemented by each filesystem supporting
casefolding, so this reduces code duplication in filesystem-specific
code.

[eugen.hristev@collabora.com: rework to first test the exact match, cleanup
and add error message]

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
Link: https://lore.kernel.org/r/20240606073353.47130-4-eugen.hristev@collabora.com
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/libfs.c b/fs/libfs.c
index b635ee5adbccede861d2fa88d7a75da496baea2a..8aa34870449fe18ce5d44ec525dd8e666de95a23 100644 (file)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1854,6 +1854,80 @@ static const struct dentry_operations generic_ci_dentry_ops = {
        .d_revalidate = fscrypt_d_revalidate,
 #endif
 };
+
+/**
+ * generic_ci_match() - Match a name (case-insensitively) with a dirent.
+ * This is a filesystem helper for comparison with directory entries.
+ * generic_ci_d_compare should be used in VFS' ->d_compare instead.
+ *
+ * @parent: Inode of the parent of the dirent under comparison
+ * @name: name under lookup.
+ * @folded_name: Optional pre-folded name under lookup
+ * @de_name: Dirent name.
+ * @de_name_len: dirent name length.
+ *
+ * Test whether a case-insensitive directory entry matches the filename
+ * being searched.  If @folded_name is provided, it is used instead of
+ * recalculating the casefold of @name.
+ *
+ * Return: > 0 if the directory entry matches, 0 if it doesn't match, or
+ * < 0 on error.
+ */
+int generic_ci_match(const struct inode *parent,
+                    const struct qstr *name,
+                    const struct qstr *folded_name,
+                    const u8 *de_name, u32 de_name_len)
+{
+       const struct super_block *sb = parent->i_sb;
+       const struct unicode_map *um = sb->s_encoding;
+       struct fscrypt_str decrypted_name = FSTR_INIT(NULL, de_name_len);
+       struct qstr dirent = QSTR_INIT(de_name, de_name_len);
+       int res = 0;
+
+       if (IS_ENCRYPTED(parent)) {
+               const struct fscrypt_str encrypted_name =
+                       FSTR_INIT((u8 *) de_name, de_name_len);
+
+               if (WARN_ON_ONCE(!fscrypt_has_encryption_key(parent)))
+                       return -EINVAL;
+
+               decrypted_name.name = kmalloc(de_name_len, GFP_KERNEL);
+               if (!decrypted_name.name)
+                       return -ENOMEM;
+               res = fscrypt_fname_disk_to_usr(parent, 0, 0, &encrypted_name,
+                                               &decrypted_name);
+               if (res < 0) {
+                       kfree(decrypted_name.name);
+                       return res;
+               }
+               dirent.name = decrypted_name.name;
+               dirent.len = decrypted_name.len;
+       }
+
+       /*
+        * Attempt a case-sensitive match first. It is cheaper and
+        * should cover most lookups, including all the sane
+        * applications that expect a case-sensitive filesystem.
+        */
+
+       if (dirent.len == name->len &&
+           !memcmp(name->name, dirent.name, dirent.len))
+               goto out;
+
+       if (folded_name->name)
+               res = utf8_strncasecmp_folded(um, folded_name, &dirent);
+       else
+               res = utf8_strncasecmp(um, name, &dirent);
+
+out:
+       kfree(decrypted_name.name);
+       if (res < 0 && sb_has_strict_encoding(sb)) {
+               pr_err_ratelimited("Directory contains filename that is invalid UTF-8");
+               return 0;
+       }
+       return !res;
+}
+EXPORT_SYMBOL(generic_ci_match);
 #endif
 
 #ifdef CONFIG_FS_ENCRYPTION

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0283cf366c2a93fd0799e7acf14973b93fb64301..2b1eeca426a045c1d579a1fa215ba772bdb0457f 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3351,6 +3351,10 @@ extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
 extern int generic_check_addressable(unsigned, u64);
 
 extern void generic_set_sb_d_ops(struct super_block *sb);
+extern int generic_ci_match(const struct inode *parent,
+                           const struct qstr *name,
+                           const struct qstr *folded_name,
+                           const u8 *de_name, u32 de_name_len);
 
 static inline bool sb_has_encoding(const struct super_block *sb)
 {