fast-import: forbid escaped NUL in paths

NUL cannot appear in paths. Even disregarding filesystem path
limitations, the tree object format delimits with NUL, so such a path
cannot be encoded by Git.

When a quoted path is unquoted, it could possibly contain NUL from
"\000". Forbid it so it isn't truncated.

fast-import still has other issues with NUL, but those will be addressed
later.

Signed-off-by: Thalia Archibald <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: thaliaarchi

Documentation/git-fast-import.txt

@@ -661,6 +661,7 @@ and its value must be in canonical form. That is it must not:
 
 The root of the tree can be represented by an empty string as `<path>`.
 
+`<path>` cannot contain NUL, either literally or escaped as `\000`.
 It is recommended that `<path>` always be encoded using UTF-8.
 
 `filedelete`

builtin/fast-import.c

@@ -2270,6 +2270,8 @@ static void parse_path(struct strbuf *sb, const char *p, const char **endp,
 	if (*p == '"') {
 		if (unquote_c_style(sb, p, endp))
 			die("Invalid %s: %s", field, command_buf.buf);
+		if (strlen(sb->buf) != sb->len)
+			die("NUL in %s: %s", field, command_buf.buf);
 	} else {
 		/*
 		 * Unless we are parsing the last field of a line,

t/t9300-fast-import.sh

@@ -3300,6 +3300,7 @@ test_path_base_fail () {
 	local change="$1" prefix="$2" field="$3" suffix="$4"
 	test_path_fail "$change" 'unclosed " in '"$field"          "$prefix" '"hello.c'    "$suffix" "Invalid $field"
 	test_path_fail "$change" "invalid escape in quoted $field" "$prefix" '"hello\xff"' "$suffix" "Invalid $field"
+	test_path_fail "$change" "escaped NUL in quoted $field"    "$prefix" '"hello\000"' "$suffix" "NUL in $field"
 }
 test_path_eol_quoted_fail () {
 	local change="$1" prefix="$2" field="$3"