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Check depth limit for nested control and meta escapes #4316

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Merged
kddnewton merged 1 commit into from
Oct 29, 2026
+39 −11
Merged

Check depth limit for nested control and meta escapes #4316

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30 changes: 19 additions & 11 deletions src/regexp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -708,11 +708,18 @@ pm_regexp_parse_hex_escape(pm_regexp_parser_t *parser) {
/**
* Parse a backslash escape sequence in a regexp, handling \u (unicode),
* \p/\P (property), \x (hex), and other single-character escapes. Also
* tracks encoding state for \M-x and \C-\M-x escapes.
* tracks encoding state for \M-x and \C-\M-x escapes. The meta and control
* forms can wrap another escape, so this recurses and is bounded by the same
* depth limit as groups and character sets.
*/
static void
pm_regexp_parse_backslash_escape(pm_regexp_parser_t *parser) {
if (pm_regexp_char_is_eof(parser)) return;
static bool
pm_regexp_parse_backslash_escape(pm_regexp_parser_t *parser, uint16_t depth) {
if (depth >= PM_REGEXP_PARSE_DEPTH_MAX) {
pm_regexp_parse_error(parser, parser->start, parser->end, "parse depth limit over");
return false;
}

if (pm_regexp_char_is_eof(parser)) return true;

switch (*parser->cursor) {
case 'u':
Expand All @@ -736,7 +743,7 @@ pm_regexp_parse_backslash_escape(pm_regexp_parser_t *parser) {
parser->cursor++;
// \M-\C-x or \M-\cx — the resulting byte is always >= 0x80
// We just need to track it as a hex escape >= 0x80.
pm_regexp_parse_backslash_escape(parser);
if (!pm_regexp_parse_backslash_escape(parser, (uint16_t) (depth + 1))) return false;
} else {
parser->cursor++;
}
Expand All @@ -754,7 +761,7 @@ pm_regexp_parse_backslash_escape(pm_regexp_parser_t *parser) {
if (!pm_regexp_char_is_eof(parser)) {
if (*parser->cursor == '\\') {
parser->cursor++;
pm_regexp_parse_backslash_escape(parser);
if (!pm_regexp_parse_backslash_escape(parser, (uint16_t) (depth + 1))) return false;
} else {
parser->cursor++;
}
Expand All @@ -769,7 +776,7 @@ pm_regexp_parse_backslash_escape(pm_regexp_parser_t *parser) {
if (!pm_regexp_char_is_eof(parser)) {
if (*parser->cursor == '\\') {
parser->cursor++;
pm_regexp_parse_backslash_escape(parser);
if (!pm_regexp_parse_backslash_escape(parser, (uint16_t) (depth + 1))) return false;
} else {
parser->cursor++;
}
Expand All @@ -780,6 +787,8 @@ pm_regexp_parse_backslash_escape(pm_regexp_parser_t *parser) {
parser->cursor++;
break;
}

return true;
}

/**
Expand Down Expand Up @@ -812,10 +821,10 @@ pm_regexp_parse_character_set(pm_regexp_parser_t *parser, uint16_t depth) {
while (!pm_regexp_char_is_eof(parser) && *parser->cursor != ']') {
switch (*parser->cursor++) {
case '[':
pm_regexp_parse_lbracket(parser, (uint16_t) (depth + 1));
if (!pm_regexp_parse_lbracket(parser, (uint16_t) (depth + 1))) return false;
break;
case '\\':
pm_regexp_parse_backslash_escape(parser);
if (!pm_regexp_parse_backslash_escape(parser, depth)) return false;
break;
default:
// We've already advanced the cursor by one byte. If the byte
Expand Down Expand Up @@ -1225,8 +1234,7 @@ pm_regexp_parse_item(pm_regexp_parser_t *parser, uint16_t depth) {
return pm_regexp_parse_quantifier(parser);
case '\\':
parser->cursor++;
pm_regexp_parse_backslash_escape(parser);
return pm_regexp_parse_quantifier(parser);
return pm_regexp_parse_backslash_escape(parser, depth) && pm_regexp_parse_quantifier(parser);
case '(':
parser->cursor++;
return pm_regexp_parse_group(parser, depth) && pm_regexp_parse_quantifier(parser);
Expand Down
20 changes: 20 additions & 0 deletions test/prism/regexp_test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -248,8 +248,28 @@ def test_newline_delimiter
assert_newline_regexp("%r\r\n\r\n", "", 0)
end

def test_depth_limit_nested_character_sets
assert_depth_limit("[" * 10_000)
end

def test_depth_limit_meta_escapes
assert_depth_limit("\\M-" * 10_000 + "a")
assert_depth_limit("[" + "\\M-" * 10_000 + "a]")
end

def test_depth_limit_control_escapes
assert_depth_limit("\\C-" * 10_000 + "a")
assert_depth_limit("\\c" * 10_000 + "a")
assert_depth_limit("[" + "\\C-" * 10_000 + "a]")
end

private

def assert_depth_limit(source)
messages = Prism.parse("/#{source}/ =~ \"\"").errors.map(&:message)
assert_equal 1, messages.count("parse depth limit over")
end

def assert_newline_regexp(source, content, options)
node = Prism.parse_statement(source)

Expand Down
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