~ chicken-core (master) fee2c0612d9fbd58909d7503d4c92bc7d4b55a86

commit fee2c0612d9fbd58909d7503d4c92bc7d4b55a86
Author:     felix <felix@call-with-current-continuation.org>
AuthorDate: Mon May 18 11:30:43 2026 +0200
Commit:     felix <felix@call-with-current-continuation.org>
CommitDate: Mon May 18 11:30:43 2026 +0200

    ensure remaining length is sufficient when decoding during utf-valudation
    
    Thanks to "phm" for pointing out this flaw.

diff --git a/utf.c b/utf.c
index 73fe8d1d..294a8ae9 100644
--- a/utf.c
+++ b/utf.c
@@ -3163,6 +3163,10 @@ static int fold2[][ 4 ] = {
  * occurs, this pointer will be a guess that depends on the particular
  * error, but it will always advance at least one byte.
  */
+
+/* (flw) quite modified and doubtlessly less branchless and optimized
+   as the original. */
+
 static const char lengths[] = {
     1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
     0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 3, 3, 4, 0
@@ -3514,9 +3518,10 @@ C_regparm C_word C_utf_validate(C_word bv, C_word blen, C_word start, C_word end
     int i = 0;
     C_u32 c;
     int e;
-    C_char *s = C_c_string(bv) + C_unfix(start), *s2;
+    unsigned char *s = C_c_string(bv) + C_unfix(start), *s2;
     int len = C_unfix(end) - C_unfix(start);
     while (len > 0) {
+        if(lengths[*s >> 3] > len) return C_SCHEME_FALSE;
         s2 = utf8_decode(s, &c, &e);
         if(e) return C_SCHEME_FALSE;
         len -= (s2 - s);