Re: [PATCH v4 1/3] elf: Allow dlopen of filter object to work [BZ #16272]

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 29/01/2020 08:17, David Kilroy wrote:
> There are two fixes that are needed to be able to dlopen filter
> objects. First _dl_map_object_deps cannot assume that map will be at
> the beginning of l_searchlist.r_list[], as filtees are inserted before
> map. Secondly dl_open_worker needs to ensure that filtees get
> relocated.
> 
> In _dl_map_object_deps:
> 
> * avoiding removing relocation dependencies of map by setting
>   l_reserved to 0 and otherwise processing the rest of the search
>   list.
> 
> * ensure 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.
> 
> Modify dl_open_worker to relocate the objects in new->l_inifini.
> new->l_initfini is constructed in _dl_map_object_deps, and lists the
> objects that need initialization and destruction. Originally the list
> of objects in new->l_next are relocated. All of these objects should
> also be included in new->l_initfini (both lists are populated with
> dependencies in _dl_map_object_deps). We can't use new->l_prev to pick
> up filtees, as during a recursive dlopen from an interposed malloc
> call, l->prev can contain objects that are not ready for relocation.
> 
> Add tests to verify that symbols resolve to the filtee implementation
> when auxiliary and filter objects are used, both as a normal link and
> when dlopen'd.
> 
> Tested by running the testsuite on x86_64.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

> ---
>  elf/Makefile               | 18 ++++++++++++++++--
>  elf/dl-deps.c              | 39 ++++++++++++++++++++++++++++----------
>  elf/dl-open.c              | 11 +++++++----
>  elf/tst-auxobj-dlopen.c    | 47 ++++++++++++++++++++++++++++++++++++++++++++++
>  elf/tst-auxobj.c           | 42 +++++++++++++++++++++++++++++++++++++++++
>  elf/tst-filterobj-aux.c    | 33 ++++++++++++++++++++++++++++++++
>  elf/tst-filterobj-dlopen.c | 39 ++++++++++++++++++++++++++++++++++++++
>  elf/tst-filterobj-filtee.c | 27 ++++++++++++++++++++++++++
>  elf/tst-filterobj-filtee.h | 24 +++++++++++++++++++++++
>  elf/tst-filterobj-flt.c    | 27 ++++++++++++++++++++++++++
>  elf/tst-filterobj.c        | 36 +++++++++++++++++++++++++++++++++++
>  11 files changed, 327 insertions(+), 16 deletions(-)
>  create mode 100644 elf/tst-auxobj-dlopen.c
>  create mode 100644 elf/tst-auxobj.c
>  create mode 100644 elf/tst-filterobj-aux.c
>  create mode 100644 elf/tst-filterobj-dlopen.c
>  create mode 100644 elf/tst-filterobj-filtee.c
>  create mode 100644 elf/tst-filterobj-filtee.h
>  create mode 100644 elf/tst-filterobj-flt.c
>  create mode 100644 elf/tst-filterobj.c
> 
> diff --git a/elf/Makefile b/elf/Makefile
> index 6c62ed6..0122431 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -201,7 +201,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
>  	 tst-unwind-ctor tst-unwind-main tst-audit13 \
>  	 tst-sonamemove-link tst-sonamemove-dlopen tst-dlopen-tlsmodid \
>  	 tst-dlopen-self tst-auditmany tst-initfinilazyfail tst-dlopenfail \
> -	 tst-dlopenfail-2
> +	 tst-dlopenfail-2 \
> +	 tst-filterobj tst-filterobj-dlopen tst-auxobj tst-auxobj-dlopen
>  #	 reldep9
>  tests-internal += loadtest unload unload2 circleload1 \
>  	 neededtest neededtest2 neededtest3 neededtest4 \

Ok.

> @@ -312,7 +313,8 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
>  		tst-auditmanymod7 tst-auditmanymod8 tst-auditmanymod9 \
>  		tst-initlazyfailmod tst-finilazyfailmod \
>  		tst-dlopenfailmod1 tst-dlopenfaillinkmod tst-dlopenfailmod2 \
> -		tst-dlopenfailmod3 tst-ldconfig-ld-mod
> +		tst-dlopenfailmod3 tst-ldconfig-ld-mod \
> +		tst-filterobj-flt tst-filterobj-aux tst-filterobj-filtee
>  # 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%,\

Ok.

> @@ -1698,3 +1700,15 @@ LDFLAGS-tst-dlopen-nodelete-reloc-mod17.so = -Wl,--no-as-needed
>  
>  $(objpfx)tst-ldconfig-ld_so_conf-update.out: $(objpfx)tst-ldconfig-ld-mod.so
>  $(objpfx)tst-ldconfig-ld_so_conf-update: $(libdl)
> +
> +LDFLAGS-tst-filterobj-flt.so = -Wl,--filter=$(objpfx)tst-filterobj-filtee.so
> +$(objpfx)tst-filterobj: $(objpfx)tst-filterobj-flt.so
> +$(objpfx)tst-filterobj-dlopen: $(libdl)
> +$(objpfx)tst-filterobj.out: $(objpfx)tst-filterobj-filtee.so
> +$(objpfx)tst-filterobj-dlopen.out: $(objpfx)tst-filterobj-filtee.so
> +
> +LDFLAGS-tst-filterobj-aux.so = -Wl,--auxiliary=$(objpfx)tst-filterobj-filtee.so
> +$(objpfx)tst-auxobj: $(objpfx)tst-filterobj-aux.so
> +$(objpfx)tst-auxobj-dlopen: $(libdl)
> +$(objpfx)tst-auxobj.out: $(objpfx)tst-filterobj-filtee.so
> +$(objpfx)tst-auxobj-dlopen.out: $(objpfx)tst-filterobj-filtee.so

Ok.

> diff --git a/elf/dl-deps.c b/elf/dl-deps.c
> index 5103a8a..0730ea9 100644
> --- a/elf/dl-deps.c
> +++ b/elf/dl-deps.c
> @@ -485,14 +485,18 @@ _dl_map_object_deps (struct link_map *map,
>  
>    map->l_searchlist.r_list = &l_initfini[nlist + 1];
>    map->l_searchlist.r_nlist = nlist;
> +  unsigned int map_index = UINT_MAX;
>  
>    for (nlist = 0, runp = known; runp; runp = runp->next)
>      {
>        if (__builtin_expect (trace_mode, 0) && runp->map->l_faked)
>  	/* This can happen when we trace the loading.  */
>  	--map->l_searchlist.r_nlist;
> -      else
> +      else {
> +	if (runp->map == map)
> +	  map_index = nlist;
>  	map->l_searchlist.r_list[nlist++] = runp->map;
> +      }
>  
>        /* Now clear all the mark bits we set in the objects on the search list
>  	 to avoid duplicates, so the next call starts fresh.  */

Ok.

> @@ -550,13 +554,14 @@ 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)

Ok.

> @@ -581,16 +586,30 @@ 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.  */
> +  assert (map_index < nlist);
> +  if (map_index > 0)
> +    {
> +      /* Copy the binary into position 0.  */
> +      l_initfini[0] = map->l_searchlist.r_list[map_index];
> +
> +      /* Copy the filtees.  */
> +      for (i = 0; i < map_index; ++i)
> +	l_initfini[i+1] = map->l_searchlist.r_list[i];
> +
> +      /* Copy the remainder.  */
> +      for (i = map_index + 1; i < nlist; ++i)
> +	l_initfini[i] = map->l_searchlist.r_list[i];
> +    }
> +  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.  */

Ok.

> diff --git a/elf/dl-open.c b/elf/dl-open.c
> index 623c975..ecb2ba9 100644
> --- a/elf/dl-open.c
> +++ b/elf/dl-open.c
> @@ -621,22 +621,25 @@ 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);

Ok.

> diff --git a/elf/tst-auxobj-dlopen.c b/elf/tst-auxobj-dlopen.c
> new file mode 100644
> index 0000000..7f91bdd
> --- /dev/null
> +++ b/elf/tst-auxobj-dlopen.c
> @@ -0,0 +1,47 @@
> +/* Test for BZ16272, dlopen'ing an auxiliary filter object.

Just a nip and tuck: usually bugzilla reports are references as BZ#NNNNN.

> +   Ensure that symbols from the resolve correctly.
> +
> +   Copyright (C) 2020 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-aux.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)");
> +
> +  fn = xdlsym (lib, "get_text2");
> +  text = fn ();
> +
> +  printf ("%s\n", text);
> +
> +  /* Verify the text matches what we expect from the auxiliary object */
> +  TEST_COMPARE_STRING (text, "Hello from auxiliary filter object (PASS)");
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>

Ok.

> diff --git a/elf/tst-auxobj.c b/elf/tst-auxobj.c
> new file mode 100644
> index 0000000..bdc7713
> --- /dev/null
> +++ b/elf/tst-auxobj.c
> @@ -0,0 +1,42 @@
> +/* Test that symbols from auxiliary filter objects are resolved to the
> +   filtee.
> +
> +   Copyright (C) 2020 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-filtee.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)");
> +
> +  text = get_text2 ();
> +  printf ("%s\n", text);
> +
> +  /* Verify the text matches what we expect from the auxiliary object */
> +  TEST_COMPARE_STRING (text, "Hello from auxiliary filter object (PASS)");
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>

Ok.

> diff --git a/elf/tst-filterobj-aux.c b/elf/tst-filterobj-aux.c
> new file mode 100644
> index 0000000..0b732f2
> --- /dev/null
> +++ b/elf/tst-filterobj-aux.c
> @@ -0,0 +1,33 @@
> +/* Auxiliary filter object.
> +   Contains symbols to be resolved in filtee, and one which doesn't.
> +
> +   Copyright (C) 2020 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-filtee.h"
> +
> +/* We never want to see the output of the auxiliary object.  */
> +const char *get_text (void)
> +{
> +  return "Hello from auxiliary filter object (FAIL)";
> +}
> +
> +/* The filtee doesn't implement this symbol, so this should resolve.  */
> +const char *get_text2 (void)
> +{
> +  return "Hello from auxiliary filter object (PASS)";
> +}

Ok.

> diff --git a/elf/tst-filterobj-dlopen.c b/elf/tst-filterobj-dlopen.c
> new file mode 100644
> index 0000000..089a3e9
> --- /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) 2020 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>

Ok.

> diff --git a/elf/tst-filterobj-filtee.c b/elf/tst-filterobj-filtee.c
> new file mode 100644
> index 0000000..817576b
> --- /dev/null
> +++ b/elf/tst-filterobj-filtee.c
> @@ -0,0 +1,27 @@
> +/* Filtee for BZ16272 test.
> +   Contains desired symbol implementations.
> +
> +   Copyright (C) 2020 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-filtee.h"
> +
> +/* This is the real implementation that wants to be called */
> +const char *get_text (void)
> +{
> +  return "Hello from filtee (PASS)";
> +}

Ok.

> diff --git a/elf/tst-filterobj-filtee.h b/elf/tst-filterobj-filtee.h
> new file mode 100644
> index 0000000..69f4749
> --- /dev/null
> +++ b/elf/tst-filterobj-filtee.h
> @@ -0,0 +1,24 @@
> +/* Filtee header for BZ16272 test.
> +   Contains prototypes for symbols implemented in the filtee.
> +
> +   Copyright (C) 2020 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);
> +
> +/* For testing auxiliary filter object.  */
> +const char *get_text2 (void);

Ok.

> diff --git a/elf/tst-filterobj-flt.c b/elf/tst-filterobj-flt.c
> new file mode 100644
> index 0000000..9da5ef1
> --- /dev/null
> +++ b/elf/tst-filterobj-flt.c
> @@ -0,0 +1,27 @@
> +/* Filter object for BZ16272 test.
> +   Contains symbols to be resolved in filtee.
> +
> +   Copyright (C) 2020 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-filtee.h"
> +
> +/* We never want to see the output of the filter object */
> +const char *get_text (void)
> +{
> +  return "Hello from filter object (FAIL)";
> +}

Ok.

> diff --git a/elf/tst-filterobj.c b/elf/tst-filterobj.c
> new file mode 100644
> index 0000000..96bfae0
> --- /dev/null
> +++ b/elf/tst-filterobj.c
> @@ -0,0 +1,36 @@
> +/* Test that symbols from filter objects are resolved to the filtee.
> +
> +   Copyright (C) 2020 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-filtee.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>
> 

Ok.