[Bug nptl/24776] pthread_key_create, pthread_setspecific are incompatible with dlmopen

["ppluzhnikov at google dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=24776

Paul Pluzhnikov <ppluzhnikov at google dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |ppluzhnikov at google dot com

--- Comment #13 from Paul Pluzhnikov <ppluzhnikov at google dot com> ---
There is a more fundamental problem with pthread_key_create from dlmopen'ed
copy of libpthread: it creates duplicate keys (since it looks in the local copy
of __pthread_keys).

The key is then used as an index into THREAD_SELF->specific_1stblock etc, which
is shared between all the namespaces, with a disastrous result.

Real-life example: https://stackoverflow.com/q/70030529

Trivial repro:

// --- cut ---
#define _GNU_SOURCE
#include <assert.h>
#include <dlfcn.h>
#include <pthread.h>

typedef int (*pthread_key_create_t)(pthread_key_t *, void (*)(void*));
int main()
{
  pthread_key_t k1, k2;
  int rc;

  rc = pthread_key_create(&k1, NULL);
  void *h = dlmopen(LM_ID_NEWLM, "libpthread.so.0", RTLD_LAZY);
  assert(h != NULL);

  pthread_key_create_t fn = (pthread_key_create_t)dlsym(h,
"pthread_key_create");
  assert(fn != NULL);

  rc = fn(&k2, NULL);
  assert(rc == 0);
  assert(k2 != k1);

  return 0;
}
// --- cut ---

gcc -g t.c -pthread -ldl -Wall -Wextra
./a.out
a.out: t.c:21: main: Assertion `k2 != k1' failed.
Aborted

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