exfat: check if filename entries exceeds max filename length

exfat_extract_uni_name copies characters from a given file name entry into
the 'uniname' variable. This variable is actually defined on the stack of
the exfat_readdir() function. According to the definition of
the 'exfat_uni_name' type, the file name should be limited 255 characters
(+ null teminator space), but the exfat_get_uniname_from_ext_entry()
function can write more characters because there is no check if filename
entries exceeds max filename length. This patch add the check not to copy
filename characters when exceeding max filename length.

Cc: [email protected]
Cc: Yuezhang Mo <[email protected]>
Reported-by: Maxim Suhanov <[email protected]>
Reviewed-by: Sungjong Seo <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>

fs/exfat/dir.c

@@ -34,6 +34,7 @@ static int exfat_get_uniname_from_ext_entry(struct super_block *sb,
 {
 	int i, err;
 	struct exfat_entry_set_cache es;
+	unsigned int uni_len = 0, len;
 
 	err = exfat_get_dentry_set(&es, sb, p_dir, entry, ES_ALL_ENTRIES);
 	if (err)
@@ -52,7 +53,10 @@ static int exfat_get_uniname_from_ext_entry(struct super_block *sb,
 		if (exfat_get_entry_type(ep) != TYPE_EXTEND)
 			break;
 
-		exfat_extract_uni_name(ep, uniname);
+		len = exfat_extract_uni_name(ep, uniname);
+		uni_len += len;
+		if (len != EXFAT_FILE_NAME_LEN || uni_len >= MAX_NAME_LENGTH)
+			break;
 		uniname += EXFAT_FILE_NAME_LEN;
 	}
 
@@ -1079,7 +1083,8 @@ rewind:
 			if (entry_type == TYPE_EXTEND) {
 				unsigned short entry_uniname[16], unichar;
 
-				if (step != DIRENT_STEP_NAME) {
+				if (step != DIRENT_STEP_NAME ||
+				    name_len >= MAX_NAME_LENGTH) {
 					step = DIRENT_STEP_FILE;
 					continue;
 				}