config: convert unbounded recursion into a loop

(cherry picked from commit a03113e8)

src/config_file.c

@@ -1349,8 +1349,9 @@ static int parse_multiline_variable(struct reader *reader, git_buf *value, int i
 {
 	char *line = NULL, *proc_line = NULL;
 	int quote_count;
-	bool multiline;
+	bool multiline = true;
 
+	while (multiline) {
 		/* Check that the next line exists */
 		line = reader_readline(reader, false);
 		if (line == NULL)
@@ -1368,9 +1369,8 @@ static int parse_multiline_variable(struct reader *reader, git_buf *value, int i
 
 		/* If it was just a comment, pretend it didn't exist */
 		if (line[0] == '\0') {
-		git__free(line);
-		return parse_multiline_variable(reader, value, quote_count);
-		/* TODO: unbounded recursion. This **could** be exploitable */
+			in_quotes = quote_count;
+			continue;
 		}
 
 		if (unescape_line(&proc_line, &multiline, line, in_quotes) < 0) {
@@ -1383,12 +1383,8 @@ static int parse_multiline_variable(struct reader *reader, git_buf *value, int i
 		git__free(line);
 		git__free(proc_line);
 
-	/*
-	 * If we need to continue reading the next line, let's just
-	 * keep putting stuff in the buffer
-	 */
-	if (multiline)
-		return parse_multiline_variable(reader, value, quote_count);
+		in_quotes = quote_count;
+	}
 
 	return 0;
 }