Avoid signed overflow in AndroidZoneInfoSource::Open offset math#360
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ravi0800 wants to merge 1 commit into
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Avoid signed overflow in AndroidZoneInfoSource::Open offset math#360ravi0800 wants to merge 1 commit into
ravi0800 wants to merge 1 commit into
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devbww
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Jul 23, 2026
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| const std::int_fast32_t start = data_offset + Decode32(ebuf + 40); | ||
| const std::int_fast64_t start = | ||
| std::int_fast64_t{data_offset} + Decode32(ebuf + 40); |
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This looks like it is being handled in #356. Please take a look there and see if you have anything to add. Otherwise we can close this PR. Thanks.
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AndroidZoneInfoSource::Open() computes a zone's file position as data_offset + Decode32(ebuf + 40), where both operands are int_fast32_t values pulled straight from the tzdata index. On a build where int_fast32_t is a 32-bit type (32-bit Android/ARM), two near-INT_MAX index values sum past the type's range, so the addition is signed overflow before the start < 0 guard on the next line ever runs. UBSan on a crafted tzdata blob reports "signed integer overflow: 76 + 2147483647 cannot be represented in type int" right at that add.
Widen the left operand to int_fast64_t so the sum is formed in a type that holds it, which leaves the existing start < 0 / length < 0 rejection meaningful and the later static_cast(start) for fseek unchanged. Doing the widening at the add keeps the fix inside the decode where the operand widths are still in view.