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fp_uscale.c: clamp parser underflow guard to POW10_MIN

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mrb_read_float's underflow short-circuit used `final_p < -342 - nd`,
which for nd > 1 can be below POW10_MIN (-343). That let
parse_decimal call prescale() with a final_p below POW10_MIN, causing
an out-of-bounds read of pow10_tab. Tighten the guard to
`final_p < POW10_MIN`; values below that threshold cannot be
represented as a non-zero double for any mantissa within the parser's
19-digit cap.

Reported by OSS-Fuzz (testcase 6097379597287424).

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2026-05-13 12:01:46 +09:00
parent 27e14c16c4
commit 403b75fbeb
2 changed files with 10 additions and 1 deletions
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src/fp_uscale.c
+1 -1
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@@ -1497,7 +1497,7 @@ mrb_read_float(const char *str, char **endp, double *fp)
else if (final_p > 308) {
res = HUGE_VAL;
}
else if (final_p < -342 - nd) {
else if (final_p < POW10_MIN) {
res = 0.0;
}
else {