[PATCH v15 3/9] libfs: Introduce case-insensitive string comparison helper

Eugen Hristev
2024-04-02T15:48:53Z

From: Gabriel Krisman Bertazi <krisman@collabora.com>

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.

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
[eugen.hristev@collabora.com: rework to first test the exact match]
Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
---
fs/libfs.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 4 +++
2 files changed, 81 insertions(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index c297953db948..711eecc125bd 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1776,6 +1776,83 @@ 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, match = 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)
+ goto out;
+ 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 (folded_name->name) {
+ if (dirent.len == folded_name->len &&
+ !memcmp(folded_name->name, dirent.name, dirent.len)) {
+ match = 1;
+ goto out;
+ }
+ res = utf8_strncasecmp_folded(um, folded_name, &dirent);
+ } else {
+ if (dirent.len == name->len &&
+ !memcmp(name->name, dirent.name, dirent.len) &&
+ (!sb_has_strict_encoding(sb) || !utf8_validate(um, name))) {
+ match = 1;
+ goto out;
+ }
+ res = utf8_strncasecmp(um, name, &dirent);
+ }
+
+out:
+ kfree(decrypted_name.name);
+ if (res < 0)
+ return res;
+ return (match || !res);
+}
+EXPORT_SYMBOL(generic_ci_match);
#endif

#ifdef CONFIG_FS_ENCRYPTION
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ff1338109b54..690b37e1db95 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3281,6 +3281,10 @@ 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)
{
--
2.34.1