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mruby-string-ext: reject surrogates and ill-formed UTF-8

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Make `Integer#chr("UTF-8")` reject UTF-16 surrogate code points
(U+D800..U+DFFF), and make `String#ord` reject ill-formed UTF-8 byte
sequences (overlong encodings, surrogates encoded as UTF-8, and code
points above U+10FFFF), matching CRuby and RFC 3629.

The `utf8code()` helper now decodes the code point first and then
validates the range per byte length:
  len=2: cp >= 0x80                 (rejects overlong)
  len=3: cp >= 0x800 and not D800..DFFF
  len=4: 0x10000 <= cp <= 0x10FFFF

close #2708

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2026-05-11 07:48:23 +09:00
parent db29955b7a
commit fe17d66363
3 changed files with 36 additions and 10 deletions
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mrbgems/mruby-string-ext/src/string.c
+17 -9
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@@ -33,7 +33,8 @@ int_chr_utf8(mrb_state *mrb, mrb_value num)
mrb_int len;
mrb_value str;
if (cp < 0 || 0x10FFFF < cp) {
/* Reject negative, above U+10FFFF, and UTF-16 surrogates (RFC 3629). */
if (cp < 0 || 0x10FFFF < cp || (0xD800 <= cp && cp <= 0xDFFF)) {
mrb_raisef(mrb, E_RANGE_ERROR, "%v out of char range", num);
}
len = mrb_utf8_to_buf(utf8, (uint32_t)cp);
@@ -973,20 +974,27 @@ utf8code(mrb_state* mrb, const unsigned char* p, const unsigned char *e)
if (p[0] < 0x80) return p[0];
mrb_int len = mrb_utf8len_table[p[0]>>3];
mrb_int cp = -1;
if (p+len <= e && len > 1 && (p[1] & 0xc0) == 0x80) {
if (len == 2)
return ((p[0] & 0x1f) << 6) + (p[1] & 0x3f);
if ((p[2] & 0xc0) == 0x80) {
cp = ((p[0] & 0x1f) << 6) + (p[1] & 0x3f);
else if ((p[2] & 0xc0) == 0x80) {
if (len == 3)
return ((p[0] & 0x0f) << 12) + ((p[1] & 0x3f) << 6)
+ (p[2] & 0x3f);
if ((p[3] & 0xc0) == 0x80) {
if (len == 4)
return ((p[0] & 0x07) << 18) + ((p[1] & 0x3f) << 12)
+ ((p[2] & 0x3f) << 6) + (p[3] & 0x3f);
cp = ((p[0] & 0x0f) << 12) + ((p[1] & 0x3f) << 6) + (p[2] & 0x3f);
else if (len == 4 && (p[3] & 0xc0) == 0x80) {
cp = ((p[0] & 0x07) << 18) + ((p[1] & 0x3f) << 12)
+ ((p[2] & 0x3f) << 6) + (p[3] & 0x3f);
}
}
}
/* Reject overlong sequences, UTF-16 surrogates, and code points above
U+10FFFF (RFC 3629, Unicode D93b). */
if (cp >= 0 &&
((len == 2 && cp >= 0x80) ||
(len == 3 && cp >= 0x800 && (cp < 0xD800 || 0xDFFF < cp)) ||
(len == 4 && cp >= 0x10000 && cp <= 0x10FFFF))) {
return cp;
}
mrb_raise(mrb, E_ARGUMENT_ERROR, "invalid UTF-8 byte sequence");
/* not reached */
return -1;