commit d0f07f7df8d9758c838674b70144ac73bcbd1634

Author: Florian Weimer <fweimer@redhat.com>

Date:   Tue May 30 13:25:50 2023 +0200

    elf: Make more functions available for binding during dlclose (bug 30425)

    Previously, after destructors for a DSO have been invoked, ld.so refused

    to bind against that DSO in all cases.  Relax this restriction somewhat

    if the referencing object is itself a DSO that is being unloaded.  This

    assumes that the symbol reference is not going to be stored anywhere.

    The situation in the test case can arise fairly easily with C++ and

    objects that are built with different optimization levels and therefore

    define different functions with vague linkage.

    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Conflicts:

	elf/Makefile

	  (usual test differences, link test with -ldl)

diff --git a/elf/Makefile b/elf/Makefile

index 634c3113227d64a6..42dc878209b11d29 100644

--- a/elf/Makefile

+++ b/elf/Makefile

@@ -362,6 +362,7 @@ tests += \

   tst-big-note \

   tst-debug1 \

   tst-deep1 \

+  tst-dlclose-lazy \

   tst-dlmodcount \

   tst-dlmopen1 \

   tst-dlmopen3 \

@@ -709,6 +710,8 @@ modules-names = \

   tst-deep1mod2 \

   tst-deep1mod3 \

   tst-dlmopen1mod \

+  tst-dlclose-lazy-mod1 \

+  tst-dlclose-lazy-mod2 \

   tst-dlmopen-dlerror-mod \

   tst-dlmopen-gethostbyname-mod \

   tst-dlmopen-twice-mod1 \

@@ -2697,3 +2700,10 @@ $(objpfx)tst-dlmopen-twice: $(libdl)

 $(objpfx)tst-dlmopen-twice.out: \

   $(objpfx)tst-dlmopen-twice-mod1.so \

   $(objpfx)tst-dlmopen-twice-mod2.so

+

+LDFLAGS-tst-dlclose-lazy-mod1.so = -Wl,-z,lazy,--no-as-needed

+$(objpfx)tst-dlclose-lazy-mod1.so: $(objpfx)tst-dlclose-lazy-mod2.so

+$(objpfx)tst-dlclose-lazy: $(libdl)

+$(objpfx)tst-dlclose-lazy.out: \

+  $(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so

+

diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c

index 47acd134600b44b5..9e8f14b8483f5eba 100644

--- a/elf/dl-lookup.c

+++ b/elf/dl-lookup.c

@@ -380,8 +380,25 @@ do_lookup_x (const char *undef_name, uint_fast32_t new_hash,

       if ((type_class & ELF_RTYPE_CLASS_COPY) && map->l_type == lt_executable)

 	continue;

-      /* Do not look into objects which are going to be removed.  */

-      if (map->l_removed)

+      /* Do not look into objects which are going to be removed,

+	 except when the referencing object itself is being removed.

+

+	 The second part covers the situation when an object lazily

+	 binds to another object while running its destructor, but the

+	 destructor of the other object has already run, so that

+	 dlclose has set l_removed.  It may not always be obvious how

+	 to avoid such a scenario to programmers creating DSOs,

+	 particularly if C++ vague linkage is involved and triggers

+	 symbol interposition.

+

+	 Accepting these to-be-removed objects makes the lazy and

+	 BIND_NOW cases more similar.  (With BIND_NOW, the symbol is

+	 resolved early, before the destructor call, so the issue does

+	 not arise.).  Behavior matches the constructor scenario: the

+	 implementation allows binding to symbols of objects whose

+	 constructors have not run.  In fact, not doing this would be

+	 mostly incompatible with symbol interposition.  */

+      if (map->l_removed && !(undef_map != NULL && undef_map->l_removed))

 	continue;

       /* Print some debugging info if wanted.  */

diff --git a/elf/tst-dlclose-lazy-mod1.c b/elf/tst-dlclose-lazy-mod1.c

new file mode 100644

index 0000000000000000..8439dc1925cc8b41

--- /dev/null

+++ b/elf/tst-dlclose-lazy-mod1.c

@@ -0,0 +1,36 @@

+/* Lazy binding during dlclose.  Directly loaded module.

+   Copyright (C) 2023 Free Software Foundation, Inc.

+   This file is part of the GNU C Library.

+

+   The GNU C Library is free software; you can redistribute it and/or

+   modify it under the terms of the GNU Lesser General Public

+   License as published by the Free Software Foundation; either

+   version 2.1 of the License, or (at your option) any later version.

+

+   The GNU C Library is distributed in the hope that it will be useful,

+   but WITHOUT ANY WARRANTY; without even the implied warranty of

+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+   Lesser General Public License for more details.

+

+   You should have received a copy of the GNU Lesser General Public

+   License along with the GNU C Library; if not, see

+   <https://www.gnu.org/licenses/>.  */

+

+/* This function is called from exported_function below.  It is only

+   defined in this module.  The weak attribute mimics how G++

+   implements vague linkage for C++.  */

+void __attribute__ ((weak))

+lazily_bound_exported_function (void)

+{

+}

+

+/* Called from tst-dlclose-lazy-mod2.so.  */

+void

+exported_function (int call_it)

+{

+  if (call_it)

+    /* Previous to the fix this would crash when called during dlclose

+       since symbols from the DSO were no longer available for binding

+       (bug 30425) after the DSO started being closed by dlclose.  */

+    lazily_bound_exported_function ();

+}

diff --git a/elf/tst-dlclose-lazy-mod2.c b/elf/tst-dlclose-lazy-mod2.c

new file mode 100644

index 0000000000000000..767f69ffdb23a685

--- /dev/null

+++ b/elf/tst-dlclose-lazy-mod2.c

@@ -0,0 +1,49 @@

+/* Lazy binding during dlclose.  Indirectly loaded module.

+   Copyright (C) 2023 Free Software Foundation, Inc.

+   This file is part of the GNU C Library.

+

+   The GNU C Library is free software; you can redistribute it and/or

+   modify it under the terms of the GNU Lesser General Public

+   License as published by the Free Software Foundation; either

+   version 2.1 of the License, or (at your option) any later version.

+

+   The GNU C Library is distributed in the hope that it will be useful,

+   but WITHOUT ANY WARRANTY; without even the implied warranty of

+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+   Lesser General Public License for more details.

+

+   You should have received a copy of the GNU Lesser General Public

+   License along with the GNU C Library; if not, see

+   <https://www.gnu.org/licenses/>.  */

+

+#include <stdio.h>

+#include <stdlib.h>

+

+void

+exported_function (int ignored)

+{

+  /* This function is interposed from tst-dlclose-lazy-mod1.so and

+     thus never called.  */

+  abort ();

+}

+

+static void __attribute__ ((constructor))

+init (void)

+{

+  puts ("info: tst-dlclose-lazy-mod2.so constructor called");

+

+  /* Trigger lazy binding to the definition in

+     tst-dlclose-lazy-mod1.so, but not for

+     lazily_bound_exported_function in that module.  */

+  exported_function (0);

+}

+

+static void __attribute__ ((destructor))

+fini (void)

+{

+  puts ("info: tst-dlclose-lazy-mod2.so destructor called");

+

+  /* Trigger the lazily_bound_exported_function call in

+     exported_function in tst-dlclose-lazy-mod1.so.  */

+  exported_function (1);

+}

diff --git a/elf/tst-dlclose-lazy.c b/elf/tst-dlclose-lazy.c

new file mode 100644

index 0000000000000000..976a6bb6f64fa981

--- /dev/null

+++ b/elf/tst-dlclose-lazy.c

@@ -0,0 +1,47 @@

+/* Test lazy binding during dlclose (bug 30425).

+   Copyright (C) 2023 Free Software Foundation, Inc.

+   This file is part of the GNU C Library.

+

+   The GNU C Library is free software; you can redistribute it and/or

+   modify it under the terms of the GNU Lesser General Public

+   License as published by the Free Software Foundation; either

+   version 2.1 of the License, or (at your option) any later version.

+

+   The GNU C Library is distributed in the hope that it will be useful,

+   but WITHOUT ANY WARRANTY; without even the implied warranty of

+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+   Lesser General Public License for more details.

+

+   You should have received a copy of the GNU Lesser General Public

+   License along with the GNU C Library; if not, see

+   <https://www.gnu.org/licenses/>.  */

+

+/* This test re-creates a situation that can arise naturally for C++

+   applications due to the use of vague linkage and differences in the

+   set of compiler-emitted functions.  A function in

+   tst-dlclose-lazy-mod1.so (exported_function) interposes a function

+   in tst-dlclose-lazy-mod2.so.  This function is called from the

+   destructor in tst-dlclose-lazy-mod2.so, after the destructor for

+   tst-dlclose-lazy-mod1.so has already completed.  Prior to the fix

+   for bug 30425, this would lead to a lazy binding failure in

+   tst-dlclose-lazy-mod1.so because dlclose had already marked the DSO

+   as unavailable for binding (by setting l_removed).  */

+

+#include <dlfcn.h>

+#include <support/xdlfcn.h>

+#include <support/check.h>

+

+int

+main (void)

+{

+  /* Load tst-dlclose-lazy-mod1.so, indirectly loading

+     tst-dlclose-lazy-mod2.so.  */

+  void *handle = xdlopen ("tst-dlclose-lazy-mod1.so", RTLD_GLOBAL | RTLD_LAZY);

+

+  /* Invoke the destructor of tst-dlclose-lazy-mod2.so, which calls

+     into tst-dlclose-lazy-mod1.so after its destructor has been

+     called.  */

+  xdlclose (handle);

+

+  return 0;

+}