[PATCH v2 1/3] elf: Allow dlopen of filter object to work [BZ #16272]

[David Kilroy <David dot Kilroy at arm dot com>]

_dl_map_object_deps assumes that map will always be at the beginning
of the search list in l_searchlist.r_list[]. This is not true if map
is a filter object, in which case the filtees are inserted before map.

Fix this by:

* avoiding relocation dependencies of map by setting l_reserved to 0
  and otherwise processing the rest of the search list.

* ensuring that map remains at the beginning of l_initfini - the list
  of things that need initialisation (and destruction). Do this by
  splitting the copy up. This may not be required, but matches the
  initialization order without dlopen.

With that in place, the filtee objects are not getting relocations
applied when dlopen is called. Modify dl_open_worker to attempt
relocations on new->l_initfini instead of objects referenced by
new->l_next (the filtees are in l_prev).

Add tests to verify that symbols resolve to the filtee implementation
when filter objects are used, both as a normal link and when dlopen'd.

Tested by running the testsuite on x86_64.
---
 elf/Makefile               | 13 +++++++++++--
 elf/dl-deps.c              | 35 ++++++++++++++++++++++++++---------
 elf/dl-open.c              | 11 +++++++----
 elf/tst-filterobj-dlopen.c | 39 +++++++++++++++++++++++++++++++++++++++
 elf/tst-filterobj-flt.c    | 24 ++++++++++++++++++++++++
 elf/tst-filterobj-lib.c    | 24 ++++++++++++++++++++++++
 elf/tst-filterobj-lib.h    | 18 ++++++++++++++++++
 elf/tst-filterobj.c        | 36 ++++++++++++++++++++++++++++++++++++
 8 files changed, 185 insertions(+), 15 deletions(-)
 create mode 100644 elf/tst-filterobj-dlopen.c
 create mode 100644 elf/tst-filterobj-flt.c
 create mode 100644 elf/tst-filterobj-lib.c
 create mode 100644 elf/tst-filterobj-lib.h
 create mode 100644 elf/tst-filterobj.c

diff --git a/elf/Makefile b/elf/Makefile
index 5e4cdb4..3292335 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -193,7 +193,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note \
 	 tst-unwind-ctor tst-unwind-main tst-audit13 \
 	 tst-sonamemove-link tst-sonamemove-dlopen tst-dlopen-tlsmodid \
-	 tst-dlopen-self
+	 tst-dlopen-self \
+	 tst-filterobj tst-filterobj-dlopen
 #	 reldep9
 tests-internal += loadtest unload unload2 circleload1 \
 	 neededtest neededtest2 neededtest3 neededtest4 \
@@ -281,7 +282,9 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib \
 		tst-absolute-zero-lib tst-big-note-lib tst-unwind-ctor-lib \
 		tst-audit13mod1 tst-sonamemove-linkmod1 \
-		tst-sonamemove-runmod1 tst-sonamemove-runmod2
+		tst-sonamemove-runmod1 tst-sonamemove-runmod2 \
+		tst-filterobj-flt tst-filterobj-lib
+
 # Most modules build with _ISOMAC defined, but those filtered out
 # depend on internal headers.
 modules-names-tests = $(filter-out ifuncmod% tst-libc_dlvsym-dso tst-tlsmod%,\
@@ -1569,3 +1572,9 @@ $(objpfx)tst-big-note-lib.so: $(objpfx)tst-big-note-lib.o
 $(objpfx)tst-unwind-ctor: $(objpfx)tst-unwind-ctor-lib.so
 
 CFLAGS-tst-unwind-main.c += -funwind-tables -DUSE_PTHREADS=0
+
+LDFLAGS-tst-filterobj-flt.so = -Wl,--filter=$(objpfx)tst-filterobj-lib.so
+$(objpfx)tst-filterobj: $(objpfx)tst-filterobj-flt.so | $(objpfx)tst-filterobj-lib.so
+$(objpfx)tst-filterobj-dlopen: $(libdl) | $(objpfx)tst-filterobj-lib.so
+$(objpfx)tst-filterobj.out: $(objpfx)tst-filterobj-lib.so
+$(objpfx)tst-filterobj-dlopen.out: $(objpfx)tst-filterobj-lib.so
diff --git a/elf/dl-deps.c b/elf/dl-deps.c
index c29b988..bb85c83 100644
--- a/elf/dl-deps.c
+++ b/elf/dl-deps.c
@@ -550,13 +550,14 @@ Filters not supported with LD_TRACE_PRELINKING"));
     }
 
   /* Maybe we can remove some relocation dependencies now.  */
-  assert (map->l_searchlist.r_list[0] == map);
   struct link_map_reldeps *l_reldeps = NULL;
   if (map->l_reldeps != NULL)
     {
-      for (i = 1; i < nlist; ++i)
+      for (i = 0; i < nlist; ++i)
 	map->l_searchlist.r_list[i]->l_reserved = 1;
 
+      /* Avoid removing relocation dependencies of the main binary.  */
+      map->l_reserved = 0;
       struct link_map **list = &map->l_reldeps->list[0];
       for (i = 0; i < map->l_reldeps->act; ++i)
 	if (list[i]->l_reserved)
@@ -581,16 +582,32 @@ Filters not supported with LD_TRACE_PRELINKING"));
 	      }
 	  }
 
-      for (i = 1; i < nlist; ++i)
+      for (i = 0; i < nlist; ++i)
 	map->l_searchlist.r_list[i]->l_reserved = 0;
     }
 
-  /* Sort the initializer list to take dependencies into account.  The binary
-     itself will always be initialize last.  */
-  memcpy (l_initfini, map->l_searchlist.r_list,
-	  nlist * sizeof (struct link_map *));
-  /* We can skip looking for the binary itself which is at the front of
-     the search list.  */
+  /* Sort the initializer list to take dependencies into account.  Always
+     initialize the binary itself last.  First, find it in the search list.  */
+  for (i = 0; i < nlist; ++i)
+    if (map->l_searchlist.r_list[i] == map)
+      break;
+  assert (i < nlist);
+  if (i > 0)
+    {
+      /* Copy the binary into position 0.  */
+      memcpy (l_initfini, &map->l_searchlist.r_list[i],
+	      sizeof (struct link_map *));
+      /* Copy the filtees.  */
+      memcpy (&l_initfini[1], map->l_searchlist.r_list,
+	      i * sizeof (struct link_map *));
+      /* Copy the remainder.  */
+      memcpy (&l_initfini[i + 1], &map->l_searchlist.r_list[i + 1],
+	      (nlist - i - 1) * sizeof (struct link_map *));
+    }
+  else
+    memcpy (l_initfini, map->l_searchlist.r_list,
+	    nlist * sizeof (struct link_map *));
+
   _dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
 
   /* Terminate the list of dependencies.  */
diff --git a/elf/dl-open.c b/elf/dl-open.c
index a9fd4cb..03f2b86 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -305,22 +305,25 @@ dl_open_worker (void *a)
      allows IFUNC relocations to work and it also means copy
      relocation of dependencies are if necessary overwritten.  */
   unsigned int nmaps = 0;
-  struct link_map *l = new;
+  unsigned int j = 0;
+  struct link_map *l = new->l_initfini[0];
   do
     {
       if (! l->l_real->l_relocated)
 	++nmaps;
-      l = l->l_next;
+      l = new->l_initfini[++j];
     }
   while (l != NULL);
+  /* Stack allocation is limited by the number of loaded objects.  */
   struct link_map *maps[nmaps];
   nmaps = 0;
-  l = new;
+  j = 0;
+  l = new->l_initfini[0];
   do
     {
       if (! l->l_real->l_relocated)
 	maps[nmaps++] = l;
-      l = l->l_next;
+      l = new->l_initfini[++j];
     }
   while (l != NULL);
   _dl_sort_maps (maps, nmaps, NULL, false);
diff --git a/elf/tst-filterobj-dlopen.c b/elf/tst-filterobj-dlopen.c
new file mode 100644
index 0000000..81eed0f
--- /dev/null
+++ b/elf/tst-filterobj-dlopen.c
@@ -0,0 +1,39 @@
+/* Test for BZ16272, dlopen'ing a filter object.
+   Ensure that symbols from the filter object resolve to the filtee.
+
+   Copyright (C) 2019 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 "support/check.h"
+#include "support/xdlfcn.h"
+
+static int do_test (void)
+{
+  void *lib = xdlopen ("tst-filterobj-flt.so", RTLD_LAZY);
+  char *(*fn)(void) = xdlsym (lib, "get_text");
+  const char* text = fn ();
+
+  printf ("%s\n", text);
+
+  /* Verify the text matches what we expect from the filtee */
+  TEST_COMPARE_STRING (text, "Hello from filtee (PASS)");
+
+  return 0;
+}
+
+#include "support/test-driver.c"
diff --git a/elf/tst-filterobj-flt.c b/elf/tst-filterobj-flt.c
new file mode 100644
index 0000000..b4e10b2
--- /dev/null
+++ b/elf/tst-filterobj-flt.c
@@ -0,0 +1,24 @@
+/* Copyright (C) 2019 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 "tst-filterobj-lib.h"
+
+/* We never want to see the output of the filter object */
+const char *get_text (void)
+{
+  return "Hello from filter object (FAIL)";
+}
diff --git a/elf/tst-filterobj-lib.c b/elf/tst-filterobj-lib.c
new file mode 100644
index 0000000..07e2348
--- /dev/null
+++ b/elf/tst-filterobj-lib.c
@@ -0,0 +1,24 @@
+/* Copyright (C) 2019 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 "tst-filterobj-lib.h"
+
+/* This is the real implementation that wants to be called */
+const char *get_text (void)
+{
+  return "Hello from filtee (PASS)";
+}
diff --git a/elf/tst-filterobj-lib.h b/elf/tst-filterobj-lib.h
new file mode 100644
index 0000000..bed9bf8
--- /dev/null
+++ b/elf/tst-filterobj-lib.h
@@ -0,0 +1,18 @@
+/* Copyright (C) 2019 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/>.  */
+
+const char *get_text (void);
diff --git a/elf/tst-filterobj.c b/elf/tst-filterobj.c
new file mode 100644
index 0000000..d38eb9b
--- /dev/null
+++ b/elf/tst-filterobj.c
@@ -0,0 +1,36 @@
+/* Test that symbols from filter objects are resolved to the filtee.
+
+   Copyright (C) 2019 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 "support/check.h"
+#include "tst-filterobj-lib.h"
+
+static int do_test (void)
+{
+  const char* text = get_text ();
+
+  printf ("%s\n", text);
+
+  /* Verify the text matches what we expect from the filtee */
+  TEST_COMPARE_STRING (text, "Hello from filtee (PASS)");
+
+  return 0;
+}
+
+#include "support/test-driver.c"
-- 
2.7.4