ksmbd: casefold utf-8 share names and fix ascii lowercase conversion

strtolower() corrupts all UTF-8 share names that have a byte in the C0
(À ISO8859-1) to DE (Þ ISO8859-1) range, since the non-ASCII part of
ISO8859-1 is incompatible with UTF-8. Prevent this by checking that a
byte is in the ASCII range with isascii(), before the conversion to
lowercase with tolower(). Properly handle case-insensitivity of UTF-8
share names by casefolding them, but fallback to ASCII lowercase
conversion on failure or if CONFIG_UNICODE is not set. Refactor to move
the share name casefolding immediately after the share name extraction.
Also, make the associated constness corrections.

Signed-off-by: Atte Heikkilä <atteh.mailbox@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 36 insertions, 8 deletions

diff --git a/fs/ksmbd/misc.c b/fs/ksmbd/misc.c
index 364a0a463dfc..28459b1efaa8 100644
--- a/fs/ksmbd/misc.c
+++ b/fs/ksmbd/misc.c
@@ -7,6 +7,7 @@
 #include <linux/kernel.h>
 #include <linux/xattr.h>
 #include <linux/fs.h>
+#include <linux/unicode.h>
 
 #include "misc.h"
 #include "smb_common.h"
@@ -226,26 +227,53 @@ void ksmbd_conv_path_to_windows(char *path)
 	strreplace(path, '/', '\\');
 }
 
+static char *casefold_sharename(struct unicode_map *um, const char *name)
+{
+	char *cf_name;
+	int cf_len;
+
+	cf_name = kzalloc(KSMBD_REQ_MAX_SHARE_NAME, GFP_KERNEL);
+	if (!cf_name)
+		return ERR_PTR(-ENOMEM);
+
+	if (IS_ENABLED(CONFIG_UNICODE) && um) {
+		const struct qstr q_name = {.name = name, .len = strlen(name)};
+
+		cf_len = utf8_casefold(um, &q_name, cf_name,
+				       KSMBD_REQ_MAX_SHARE_NAME);
+		if (cf_len < 0)
+			goto out_ascii;
+
+		return cf_name;
+	}
+
+out_ascii:
+	cf_len = strscpy(cf_name, name, KSMBD_REQ_MAX_SHARE_NAME);
+	if (cf_len < 0) {
+		kfree(cf_name);
+		return ERR_PTR(-E2BIG);
+	}
+
+	for (; *cf_name; ++cf_name)
+		*cf_name = isascii(*cf_name) ? tolower(*cf_name) : *cf_name;
+	return cf_name - cf_len;
+}
+
 /**
  * ksmbd_extract_sharename() - get share name from tree connect request
  * @treename:	buffer containing tree name and share name
  *
  * Return:      share name on success, otherwise error
  */
-char *ksmbd_extract_sharename(char *treename)
+char *ksmbd_extract_sharename(struct unicode_map *um, const char *treename)
 {
-	char *name = treename;
-	char *dst;
-	char *pos = strrchr(name, '\\');
+	const char *name = treename, *pos = strrchr(name, '\\');
 
 	if (pos)
 		name = (pos + 1);
 
 	/* caller has to free the memory */
-	dst = kstrdup(name, GFP_KERNEL);
-	if (!dst)
-		return ERR_PTR(-ENOMEM);
-	return dst;
+	return casefold_sharename(um, name);
 }
 
 /**