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commit 9f55d2e7c42e6ca862a25d3ee3eb2b367811c30d
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Author: Florian Weimer <fweimer@redhat.com>
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Date:   Fri Oct 14 12:43:07 2022 +0200
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    elf: Do not completely clear reused namespace in dlmopen (bug 29600)
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    The data in the _ns_debug member must be preserved, otherwise
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    _dl_debug_initialize enters an infinite loop.  To be conservative,
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    only clear the libc_map member for now, to fix bug 29528.
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    Fixes commit d0e357ff45a75553dee3b17ed7d303bfa544f6fe
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    ("elf: Call __libc_early_init for reused namespaces (bug 29528)"),
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    by reverting most of it.
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    Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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    Tested-by: Carlos O'Donell <carlos@redhat.com>
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    (cherry picked from commit 2c42257314536b94cc8d52edede86e94e98c1436)
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    (Conflict in elf/dl-open.c due to missing _r_debug namespace support.)
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diff --git a/elf/dl-open.c b/elf/dl-open.c
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index 1ab3c7b5ac2fbc45..633b047ad2497296 100644
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--- a/elf/dl-open.c
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+++ b/elf/dl-open.c
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@@ -839,15 +839,13 @@ _dl_open (const char *file, int mode, const void *caller_dlopen, Lmid_t nsid,
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 	  _dl_signal_error (EINVAL, file, NULL, N_("\
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 no more namespaces available for dlmopen()"));
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 	}
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+      else if (nsid == GL(dl_nns))
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+	{
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+	  __rtld_lock_initialize (GL(dl_ns)[nsid]._ns_unique_sym_table.lock);
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+	  ++GL(dl_nns);
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+	}
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-      if (nsid == GL(dl_nns))
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-	++GL(dl_nns);
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-
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-      /* Initialize the new namespace.  Most members are
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-	 zero-initialized, only the lock needs special treatment.  */
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-      memset (&GL(dl_ns)[nsid], 0, sizeof (GL(dl_ns)[nsid]));
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-      __rtld_lock_initialize (GL(dl_ns)[nsid]._ns_unique_sym_table.lock);
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-
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+      GL(dl_ns)[nsid].libc_map = NULL;
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       _dl_debug_initialize (0, nsid)->r_state = RT_CONSISTENT;
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     }
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   /* Never allow loading a DSO in a namespace which is empty.  Such
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diff --git a/elf/tst-dlmopen-twice.c b/elf/tst-dlmopen-twice.c
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index 449f3c8fa9f2aa01..70c71fe19c7d0bf9 100644
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--- a/elf/tst-dlmopen-twice.c
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+++ b/elf/tst-dlmopen-twice.c
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@@ -16,18 +16,38 @@
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    License along with the GNU C Library; if not, see
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    <https://www.gnu.org/licenses/>.  */
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-#include <support/xdlfcn.h>
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+#include <stdio.h>
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 #include <support/check.h>
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+#include <support/xdlfcn.h>
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-static int
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-do_test (void)
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+/* Run the test multiple times, to check finding a new namespace while
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+   another namespace is already in use.  This used to trigger bug 29600.  */
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+static void
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+recurse (int depth)
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 {
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-  void *handle = xdlmopen (LM_ID_NEWLM, "tst-dlmopen-twice-mod1.so", RTLD_NOW);
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+  if (depth == 0)
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+    return;
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+
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+  printf ("info: running at depth %d\n", depth);
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+  void *handle = xdlmopen (LM_ID_NEWLM, "tst-dlmopen-twice-mod1.so",
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+                           RTLD_NOW);
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   xdlclose (handle);
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   handle = xdlmopen (LM_ID_NEWLM, "tst-dlmopen-twice-mod2.so", RTLD_NOW);
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   int (*run_check) (void) = xdlsym (handle, "run_check");
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   TEST_COMPARE (run_check (), 0);
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+  recurse (depth - 1);
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   xdlclose (handle);
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+}
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+
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+static int
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+do_test (void)
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+{
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+  /* First run the test without nesting.  */
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+  recurse (1);
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+
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+  /* Then with nesting.  The constant needs to be less than the
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+     internal DL_NNS namespace constant.  */
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+  recurse (10);
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   return 0;
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 }
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