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Subject:	Re: SIGSEGV in pthread_testcancel() likely due to NULL TLS access
	(Re: A process spawned inside gem command running on latest ruby segfaults)
To:	cygwin AT cygwin DOT com
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From:	Daisuke Fujimura via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Daisuke Fujimura <booleanlabel AT gmail DOT com>
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I tried running a ruby program with openssl-3.0.16-2, and confirmed
that the SIGSEGV no longer occurs. Thank you for the advice.

On Mon, Jun 23, 2025 at 2:04 AM Jeremy Drake <cygwin AT jdrake DOT com> wrote:
>
> On Sun, 22 Jun 2025, Daisuke Fujimura via Cygwin wrote:
>
> > The reproduction procedure could be simplified.
> >
> > A segmentation fault (SIGSEGV) occurs when running a Ruby script using
> > Ruby 3.4.2 (test package) on Cygwin 3.6.3-1 (x86_64), where Thread.new
> > is used to require 'openssl' inside a thread.
> >
> > The crash path leads from OpenSSL’s OPENSSL_thread_stop() to
> > CRYPTO_THREAD_write_lock() and then pthread_rwlock_wrlock(), which
> > invokes pthread_testcancel(). At that point, a NULL pointer
> > dereference seems to occur, possibly during access to TLS data.
> >
> > Thread 8 "repro.rb:1" received signal SIGSEGV, Segmentation fault.
> > [Switching to Thread 7380.0x25e4]
> > 0x0000000000000000 in ?? ()
> > (gdb) where
> > #0 0x0000000000000000 in ?? ()
> > #1 0x00007ffe4ad2a0e4 in pthread_testcancel () at
> > /usr/src/debug/cygwin-3.6.3-1/winsup/cygwin/thread.cc:399
> > #2 pthread_rwlock_wrlock (rwlock=0xa002a9010) at
> > /usr/src/debug/cygwin-3.6.3-1/winsup/cygwin/thread.cc:4352
> > #3 0x00007ffe4ae0b0d4 in _sigfe () at sigfe.s:35
> > #4 0x00000003ff54e3f9 in CRYPTO_THREAD_write_lock (lock=<optimized
> > out>) at crypto/threads_pthread.c:110
> > #5 0x00000003ff541922 in init_thread_remove_handlers
> > (handsin=handsin AT entry=0x0) at crypto/initthread.c:178
> > #6 0x00000003ff541d43 in OPENSSL_thread_stop () at crypto/initthread.c:235
> > #7 0x00000003ff53fdd3 in DllMain (hinstDLL=<optimized out>,
> > fdwReason=<optimized out>, lpvReserved=<optimized out>)
> > at crypto/dllmain.c:38
> > #8 0x00007ffe8f2fd6ac in ?? ()
> > #9 0x00007ffe8f38b590 in ?? ()
> > #10 0x00007ffe8f38b590 in ?? ()
> > #11 0x0000000000000000 in ?? ()
>
> This should be fixed by test release openssl-3.0.16-2
> (https://cygwin.com/pipermail/cygwin-announce/2025-May/012341.html).  I
> don't know what the plan is for making that stable, or getting a patch
> upstream.

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