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parser.c: Ensure the user provided string can't be mutated #985

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Merged
byroot merged 1 commit into from
May 28, 2026
+39 −15
Merged

parser.c: Ensure the user provided string can't be mutated #985

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38 changes: 23 additions & 15 deletions ext/json/ext/parser/parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1457,18 +1457,21 @@ static void json_ensure_eof(JSON_ParserState *state)

static VALUE convert_encoding(VALUE source)
{
int encindex = RB_ENCODING_GET(source);
StringValue(source);
int encindex = RB_ENCODING_GET(source);

if (RB_LIKELY(encindex == utf8_encindex)) {
return source;
}
if (RB_LIKELY(encindex == utf8_encindex)) {
return source;
}

if (encindex == binary_encindex) {
// For historical reason, we silently reinterpret binary strings as UTF-8
return rb_enc_associate_index(rb_str_dup(source), utf8_encindex);
}
if (encindex == binary_encindex) {
// For historical reason, we silently reinterpret binary strings as UTF-8
return rb_enc_associate_index(rb_str_dup(source), utf8_encindex);
}

return rb_funcall(source, i_encode, 1, Encoding_UTF_8);
source = rb_funcall(source, i_encode, 1, Encoding_UTF_8);
StringValue(source);
return source;
}

struct parser_config_init_args {
Expand Down Expand Up @@ -1583,10 +1586,16 @@ static VALUE cParserConfig_initialize(VALUE self, VALUE opts)
return self;
}

static VALUE cParser_parse(JSON_ParserConfig *config, VALUE Vsource)
static VALUE cParser_parse(JSON_ParserConfig *config, VALUE src)
{
Vsource = convert_encoding(StringValue(Vsource));
StringValue(Vsource);
VALUE Vsource = convert_encoding(src);

// Ensure the string isn't mutated under us.
// The classic API to use is `rb_str_locktmp`, but then we'd
// need to use `rb_protect` to make sure we always unlock.
if (Vsource == src) {
Vsource = rb_str_new_frozen(Vsource);
}

VALUE rvalue_stack_buffer[RVALUE_STACK_INITIAL_CAPA];
rvalue_stack stack = {
Expand All @@ -1597,6 +1606,7 @@ static VALUE cParser_parse(JSON_ParserConfig *config, VALUE Vsource)

long len;
const char *start;

RSTRING_GETMEM(Vsource, start, len);

VALUE stack_handle = 0;
Expand All @@ -1615,6 +1625,7 @@ static VALUE cParser_parse(JSON_ParserConfig *config, VALUE Vsource)
// it won't cause a leak.
rvalue_stack_eagerly_release(stack_handle);
RB_GC_GUARD(stack_handle);
RB_GC_GUARD(Vsource);
json_ensure_eof(state);

return result;
Expand All @@ -1635,9 +1646,6 @@ static VALUE cParserConfig_parse(VALUE self, VALUE Vsource)

static VALUE cParser_m_parse(VALUE klass, VALUE Vsource, VALUE opts)
{
Vsource = convert_encoding(StringValue(Vsource));
StringValue(Vsource);

JSON_ParserConfig _config = {0};
JSON_ParserConfig *config = &_config;
parser_config_init(config, opts, false);
Expand Down
16 changes: 16 additions & 0 deletions test/json/json_parser_test.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -878,6 +878,22 @@ def test_frozen
end
end

def test_mutating_source_string_during_parsing
expected = ([1] * 100) + [2.3] + ([1] * 100)
source = JSON.generate(expected)
expected.delete_at(100)

fake_decimal_class = Class.new
fake_decimal_class.define_method(:initialize) do |number|
source.tr!('1', '0')
number.to_f
end

actual = JSON.parse(source, decimal_class: fake_decimal_class)
actual.delete_at(100)
assert_equal expected, actual
end

private

def assert_equal_float(expected, actual, delta = 1e-2)
Expand Down