Re: [PATCH v3 1/3] elf: Allow dlopen of filter object to work [BZ #16272]

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

On 03/12/2019 14:30, 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 relocatiion dependencies of map by setting

s/relocatiion/relocation

>   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 filter objects are used, both as a normal link and when dlopen'd.

Since these are the only filter tests, I think we should also add some
minimal one to check for invalid filter filter object (which does not
provide the required symbol interfaces provided by the filtee).

I think also it is worth to extend the tests to cover for auxiliary
filters as well (DT_AUXILIARY), since it intersects with DT_FILTERS.
It should be similar to DT_FILTER tests, with the only difference 
that non existent auxiliary filters does not trigger a loader error
(if the symbol is provided by the filter or another auxiliary filter).

The patch itself looks good, thanks for working on it. 

> 
> Tested by running the testsuite on x86_64.
> ---
>  elf/Makefile               | 12 ++++++++++--
>  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, 184 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 0debea7..69f11c7 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -199,7 +199,8 @@ 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-auditmany tst-initfinilazyfail tst-dlopenfail
> +	 tst-dlopen-self tst-auditmany tst-initfinilazyfail tst-dlopenfail \
> +	 tst-filterobj tst-filterobj-dlopen
>  #	 reldep9
>  tests-internal += loadtest unload unload2 circleload1 \
>  	 neededtest neededtest2 neededtest3 neededtest4 \

Ok.

> @@ -292,7 +293,8 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
>  		tst-auditmanymod4 tst-auditmanymod5 tst-auditmanymod6 \
>  		tst-auditmanymod7 tst-auditmanymod8 tst-auditmanymod9 \
>  		tst-initlazyfailmod tst-finilazyfailmod \
> -		tst-dlopenfailmod1 tst-dlopenfaillinkmod tst-dlopenfailmod2
> +		tst-dlopenfailmod1 tst-dlopenfaillinkmod tst-dlopenfailmod2 \
> +		tst-filterobj-flt tst-filterobj-lib

Ok.

>  # 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%,\
> @@ -1627,3 +1629,9 @@ $(objpfx)tst-dlopenfailmod1.so: \
>    $(shared-thread-library) $(objpfx)tst-dlopenfaillinkmod.so
>  LDFLAGS-tst-dlopenfaillinkmod.so = -Wl,-soname,tst-dlopenfail-missingmod.so
>  $(objpfx)tst-dlopenfailmod2.so: $(shared-thread-library)
> +
> +LDFLAGS-tst-filterobj-flt.so = -Wl,--filter=$(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

I think there is no need need to set the tst-filterobj* to be order-only
here, afaik we don't currently support issuing the 'check' without a 
full build if the tree is updated. I am not sure if order-only prerequisite
here would make some difference.

> 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);

Ok, the first entry is the filtee object.

>    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;
>      }

I am trying to understand why we can't skip first element here. Neither
of the tests actually exercise this code patch (they won't add a
dependency on l_reldeps), so could you provide an example/testcase
where it requires such change?

>  
> -  /* 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;

Ok. I am not sure if it is worth the optimization trouble, but one option
might be to compute the 'map' index while 'map->l_searchlist.r_list' is
being set while iterating over 'known' maps (loop at line 489).

> +  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 *));

Ok (although I not sure if is the correct idiom to use memcpy to
copy array of pointers).


> +    }
> +  else
> +    memcpy (l_initfini, map->l_searchlist.r_list,
> +	    nlist * sizeof (struct link_map *));
> +

Ok

>    _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 df9f29a..9996fe9 100644
> --- a/elf/dl-open.c
> +++ b/elf/dl-open.c
> @@ -637,22 +637,25 @@ 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);

Ok.

> +  /* 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-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.

Update Copyright year to 2020.

> +   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 (although we usually use '<' for support files).

> 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.

Missing one line description and Copyright year update to 2020.

> +   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)";
> +}

Ok.

> 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.

Missing one line description and Copyright year update to 2020.

> +   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)";
> +}

Ok.

> 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.

Missing one line description and Copyright year update to 2020.

> +   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);

Ok.

> 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.

Update Copyright year to 2020.

> +   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"
> 

Ok.