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  1. RHEL
  2. RHEL-72011

glibc: ctype.h macros segfault in multithreaded programs with multiple libc.so [rhel-8]

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      .glibc: `ctype.h` macros caused segmentation faults in multithreaded programs with multiple `libc.so`

      Previously, the internal state for ‎`<ctype.h>` in secondary C library copies created by audit or with ‎`dlmopen` failed to initialize for threads created with ‎`pthread_create`. As a consequence, using ‎`<ctype.h>` functionality, either directly or indirectly, in secondary threads and namespaces resulted in program crashes.

      With this update, the internal state for ‎`<ctype.h>` is initialized to refer to the ‎`C` locale for secondary threads and namespaces. As a result, using functionality from ‎`<ctype.h>` in these scenarios no longer causes crashes.
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      .glibc: `ctype.h` macros caused segmentation faults in multithreaded programs with multiple `libc.so` Previously, the internal state for ‎`<ctype.h>` in secondary C library copies created by audit or with ‎`dlmopen` failed to initialize for threads created with ‎`pthread_create`. As a consequence, using ‎`<ctype.h>` functionality, either directly or indirectly, in secondary threads and namespaces resulted in program crashes. With this update, the internal state for ‎`<ctype.h>` is initialized to refer to the ‎`C` locale for secondary threads and namespaces. As a result, using functionality from ‎`<ctype.h>` in these scenarios no longer causes crashes.
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      The ctype.h macros (isdigit, isspace, etc.) segfault if called from a secondary thread (created in the base namespace) and dlmopen'd namespace.

      In this scenario `*_ctype_b_loc()` is a zero pointer which causes the segfault. AFAICT `_ctype_init()` is only called for the base namespace during `start_thread()`, the dlmopen'd namespace's locale TLS is left default-initialized to a zero pointer that then gets dereferenced in the `isdigit()` macro and segfaults.

       

      This has already been filed upstream https://sourceware.org/bugzilla/show_bug.cgi?id=32483 and appears to affect all versions of glibc including upstream glibc.

      A RH glibc engineer has already done an initial evaluation and posted a patch upstream https://sourceware.org/pipermail/libc-alpha/2024-December/162893.html

      The customer request is to backport this upstream patch and include it in RHEL8.10 (current production), RHEL 9.5 (currently in testing), and make sure that it is included in RHEL10.

       

      Kindly let me know if we need to raise separate Jira's for RHEL 9 and RHEL 10.

       

      Also, the customer has shared reproducer programs as attachment "reproducer.tar.gz" which I have attached to this Jira now.

        1. reproducer.tar.gz
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          Virendrasingh Rajput

              glibc-bugzilla Platform Tools - Libraries Bot
              rhn-support-vrajput Virendrasingh Rajput
              Michal Stubna
              Platform Tools - Libraries Bot Platform Tools - Libraries Bot
              Martin Coufal Martin Coufal
              Malhar Jivrajani Malhar Jivrajani
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