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Memory leak in hmac module with HACL* backend detected by AddressSanitizer #140120

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Memory leak in hmac module with HACL* backend detected by AddressSanitizer#140120
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gpshead
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3.14bugs and security fixesextension-modulesC modules in the Modules dirperformancePerformance or resource usagetype-bugAn unexpected behavior, bug, or error

Description

@ashm-dev
ashm-dev
opened on Oct 14, 2025

Bug report

Bug Description:

A memory leak has been detected in the hmac module when running test_hmac. The issue appears to be specific to the Hacl_Streaming_HMAC implementation, as indicated by the stack traces from the AddressSanitizer (ASan) report. The leaks occur within functions responsible for HMAC digest computation (_Py_LibHacl_Hacl_Streaming_HMAC_digest, hmac_digest_compute_locked), suggesting that memory allocated during these operations is not being properly deallocated.

Steps to Reproduce:

  1. Configure the build with the following flags to enable debugging and AddressSanitizer:

    CC=clang CXX=clang++ \
./configure \
--disable-optimizations \
--with-valgrind \
--with-pydebug \
--enable-pystats \
--with-address-sanitizer

  2. Build CPython:

    make -j$(nproc)

  3. Run the hmac test suite:

    ./python -m test test_hmac

System Information:

  • OS: Ubuntu 25.04 (Plucky Puffin)
  • Kernel: Linux huawei 6.14.0-33-generic #33-Ubuntu SMP PREEMPT_DYNAMIC Wed Sep 17 23:22:02 UTC 2025 x86_64
  • Clang Version: Ubuntu clang version 20.1.2 (0ubuntu1)

ASan Leak Report:

test.log

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

Activity

  1. ashm-dev
    added
    type-bugAn unexpected behavior, bug, or error
    on Oct 14, 2025
  2. StanFromIreland
    added
    performancePerformance or resource usage
    extension-modulesC modules in the Modules dir
    on Oct 14, 2025

  3. gpshead commented on Oct 14, 2025

    @gpshead
    gpshead
    on Oct 14, 2025
    Member

    patch from upstream hacl* needed - #140124 (comment)

  4. protz commented on Oct 15, 2025

    @protz
    protz
    on Oct 15, 2025
    Contributor

    Thanks for the heads-up. Is there any more precise information as to where the issue occurs? Do we know which allocation is not freed?

    CC @R1kM

  5. protz commented on Oct 15, 2025

    @protz
    protz
    on Oct 15, 2025
    Contributor

    Oh I see the patch is in https://github.com/python/cpython/pull/140124/files -- let me look into this.

  6. protz commented on Oct 15, 2025

    @protz
    protz
    on Oct 15, 2025
    Contributor

    hacl-star/hacl-star#1064 has been merged so the next refresh of HACL* will have the fix. Thanks for reporting!

  7. gpshead
    self-assigned this
    on Oct 16, 2025
  8. gpshead
    added a commit that references this issue on Oct 16, 2025

    gh-140120: Refresh HACL* to fix an hmac memory leak (GH-140188)

    3a81313
  9. miss-islington
    added a commit that references this issue on Oct 16, 2025

    pythongh-140120: Refresh HACL* to fix an hmac memory leak (pythonGH-1…

    c1dc5eb

  10. ashm-dev commented on Oct 16, 2025

    @ashm-dev
    ashm-dev
    on Oct 16, 2025
    ContributorAuthor

    I checked, there are no more leaks, thank you!

  11. gpshead
    added a commit that references this issue on Oct 17, 2025

    [3.14] gh-140120: Refresh HACL* to fix an hmac memory leak (GH-140188) (

    32e60fa

  12. gpshead commented on Oct 17, 2025

    @gpshead
    gpshead
    on Oct 17, 2025
    Member

    yay, thanks for finding this!

  13. gpshead
    closed this as completedon Oct 17, 2025
  14. gpshead
    added
    3.14bugs and security fixes
    on Oct 17, 2025
  15. StanFromIreland
    added a commit that references this issue on Dec 6, 2025

    pythongh-140120: Refresh HACL* to fix an hmac memory leak (pythonGH-1…

    e417226
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