feefrac test: avoid integer overflow (bugfix) #32240

1. 
   sipa commented at 7:20 pm on April 8, 2025: member

   The feefrac_mul_div fuzz test fails after #30535 with the following (base64) input: Nb6Fc/97AACAAAD/ewAAgAAAAIAAAACAAAAAoA== (see https://cirrus-ci.com/task/5240029192126464?logs=ci#L3353).

   This is caused by an internal multiplication inside CFeeRate that just exceeds the limit of the int64_t type. Fix that by tightening the bounds slightly further.

2. feefrac test: avoid integer overflow (bugfix) a2bc330da8
3. 
   DrahtBot commented at 7:21 pm on April 8, 2025: contributor

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   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32240.

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4. 
   sipa commented at 7:21 pm on April 8, 2025: member

   cc @sr-gi
5. sipa requested review from Copilot on Apr 8, 2025
6. 
   Copilot commented at 8:02 pm on April 8, 2025: none

   Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

   src/test/fuzz/feefrac.cpp:223

   • The change from non-strict to strict inequalities correctly prevents borderline overflow conditions. Please verify that these adjustments do not inadvertently exclude valid cases that were intended to be processed.

   0if (mul64 < std::numeric_limits<int64_t>::max() / 1000 &&
   

7. 
   sipa commented at 8:02 pm on April 8, 2025: member

   Thanks, Copilot.
8. laanwj added the label Tests on Apr 9, 2025
9. instagibbs approved
10. 
    instagibbs commented at 3:14 pm on April 9, 2025: member

    ACK a2bc330da86b604069308f5237b77cfa77ed2b43

    Can confirm it was allowing one-too-large values for the computed CAmount, and that it fails on master.

11. 
    sr-gi commented at 3:21 pm on April 9, 2025: member

    utACK a2bc330da86b604069308f5237b77cfa77ed2b43

    Trying to reproduce on my local setup, which is proving challenging (macOS).

    I’ll report later if I’m able to trigger it

12. 
    glozow commented at 6:26 pm on April 9, 2025: member

    ACK a2bc330da86b604069308f5237b77cfa77ed2b43, was able to reproduce + verify this fix
13. glozow merged this on Apr 9, 2025
14. glozow closed this on Apr 9, 2025

    ---

15. 
    sr-gi commented at 2:04 pm on April 10, 2025: member

    post-merge ACK, was able to reproduce locally and verify it doesn’t crash anymore after the patch

Contributors
sipa DrahtBot Copilot instagibbs sr-gi glozow

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