xref: /elf/dl-deps.c

/* Load the dependencies of a mapped object.
   Copyright (C) 1996-2021 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 <atomic.h>
#include <assert.h>
#include <dlfcn.h>
#include <errno.h>
#include <libintl.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/param.h>
#include <ldsodefs.h>
#include <scratch_buffer.h>

#include <dl-dst.h>

/* Whether an shared object references one or more auxiliary objects
   is signaled by the AUXTAG entry in l_info.  */
#define AUXTAG	(DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM \
		 + DT_EXTRATAGIDX (DT_AUXILIARY))
/* Whether an shared object references one or more auxiliary objects
   is signaled by the AUXTAG entry in l_info.  */
#define FILTERTAG (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM \
		   + DT_EXTRATAGIDX (DT_FILTER))


/* When loading auxiliary objects we must ignore errors.  It's ok if
   an object is missing.  */
struct openaux_args
  {
    /* The arguments to openaux.  */
    struct link_map *map;
    int trace_mode;
    int open_mode;
    const char *strtab;
    const char *name;

    /* The return value of openaux.  */
    struct link_map *aux;
  };

static void
openaux (void *a)
{
  struct openaux_args *args = (struct openaux_args *) a;

  args->aux = _dl_map_object (args->map, args->name,
			      (args->map->l_type == lt_executable
			       ? lt_library : args->map->l_type),
			      args->trace_mode, args->open_mode,
			      args->map->l_ns);
}

static ptrdiff_t
_dl_build_local_scope (struct link_map **list, struct link_map *map)
{
  struct link_map **p = list;
  struct link_map **q;

  *p++ = map;
  map->l_reserved = 1;
  if (map->l_initfini)
    for (q = map->l_initfini + 1; *q; ++q)
      if (! (*q)->l_reserved)
	p += _dl_build_local_scope (p, *q);
  return p - list;
}


/* We use a very special kind of list to track the path
   through the list of loaded shared objects.  We have to
   produce a flat list with unique members of all involved objects.
*/
struct list
  {
    int done;			/* Nonzero if this map was processed.  */
    struct link_map *map;	/* The data.  */
    struct list *next;		/* Elements for normal list.  */
  };


/* Macro to expand DST.  It is an macro since we use `alloca'.  */
#define expand_dst(l, str, fatal) \
  ({									      \
    const char *__str = (str);						      \
    const char *__result = __str;					      \
    size_t __dst_cnt = _dl_dst_count (__str);				      \
									      \
    if (__dst_cnt != 0)							      \
      {									      \
	char *__newp;							      \
									      \
	/* DST must not appear in SUID/SGID programs.  */		      \
	if (__libc_enable_secure)					      \
	  _dl_signal_error (0, __str, NULL, N_("\
DST not allowed in SUID/SGID programs"));				      \
									      \
	__newp = (char *) alloca (DL_DST_REQUIRED (l, __str, strlen (__str),  \
						   __dst_cnt));		      \
									      \
	__result = _dl_dst_substitute (l, __str, __newp);		      \
									      \
	if (*__result == '\0')						      \
	  {								      \
	    /* The replacement for the DST is not known.  We can't	      \
	       processed.  */						      \
	    if (fatal)							      \
	      _dl_signal_error (0, __str, NULL, N_("\
empty dynamic string token substitution"));				      \
	    else							      \
	      {								      \
		/* This is for DT_AUXILIARY.  */			      \
		if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))   \
		  _dl_debug_printf (N_("\
cannot load auxiliary `%s' because of empty dynamic string token "	      \
					    "substitution\n"), __str);	      \
		continue;						      \
	      }								      \
	  }								      \
      }									      \
									      \
    __result; })

static void
preload (struct list *known, unsigned int *nlist, struct link_map *map)
{
  known[*nlist].done = 0;
  known[*nlist].map = map;
  known[*nlist].next = &known[*nlist + 1];

  ++*nlist;
  /* We use `l_reserved' as a mark bit to detect objects we have
     already put in the search list and avoid adding duplicate
     elements later in the list.  */
  map->l_reserved = 1;
}

void
_dl_map_object_deps (struct link_map *map,
		     struct link_map **preloads, unsigned int npreloads,
		     int trace_mode, int open_mode)
{
  struct list *known = __alloca (sizeof *known * (1 + npreloads + 1));
  struct list *runp, *tail;
  unsigned int nlist, i;
  /* Object name.  */
  const char *name;
  int errno_saved;
  int errno_reason;
  struct dl_exception exception;

  /* No loaded object so far.  */
  nlist = 0;

  /* First load MAP itself.  */
  preload (known, &nlist, map);

  /* Add the preloaded items after MAP but before any of its dependencies.  */
  for (i = 0; i < npreloads; ++i)
    preload (known, &nlist, preloads[i]);

  /* Terminate the lists.  */
  known[nlist - 1].next = NULL;

  /* Pointer to last unique object.  */
  tail = &known[nlist - 1];

  struct scratch_buffer needed_space;
  scratch_buffer_init (&needed_space);

  /* Process each element of the search list, loading each of its
     auxiliary objects and immediate dependencies.  Auxiliary objects
     will be added in the list before the object itself and
     dependencies will be appended to the list as we step through it.
     This produces a flat, ordered list that represents a
     breadth-first search of the dependency tree.

     The whole process is complicated by the fact that we better
     should use alloca for the temporary list elements.  But using
     alloca means we cannot use recursive function calls.  */
  errno_saved = errno;
  errno_reason = 0;
  errno = 0;
  name = NULL;
  for (runp = known; runp; )
    {
      struct link_map *l = runp->map;
      struct link_map **needed = NULL;
      unsigned int nneeded = 0;

      /* Unless otherwise stated, this object is handled.  */
      runp->done = 1;

      /* Allocate a temporary record to contain the references to the
	 dependencies of this object.  */
      if (l->l_searchlist.r_list == NULL && l->l_initfini == NULL
	  && l != map && l->l_ldnum > 0)
	{
	  /* l->l_ldnum includes space for the terminating NULL.  */
	  if (!scratch_buffer_set_array_size
	      (&needed_space, l->l_ldnum, sizeof (struct link_map *)))
	    _dl_signal_error (ENOMEM, map->l_name, NULL,
			      N_("cannot allocate dependency buffer"));
	  needed = needed_space.data;
	}

      if (l->l_info[DT_NEEDED] || l->l_info[AUXTAG] || l->l_info[FILTERTAG])
	{
	  const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
	  struct openaux_args args;
	  struct list *orig;
	  const ElfW(Dyn) *d;

	  args.strtab = strtab;
	  args.map = l;
	  args.trace_mode = trace_mode;
	  args.open_mode = open_mode;
	  orig = runp;

	  for (d = l->l_ld; d->d_tag != DT_NULL; ++d)
	    if (__builtin_expect (d->d_tag, DT_NEEDED) == DT_NEEDED)
	      {
		/* Map in the needed object.  */
		struct link_map *dep;

		/* Recognize DSTs.  */
		name = expand_dst (l, strtab + d->d_un.d_val, 0);
		/* Store the tag in the argument structure.  */
		args.name = name;

		int err = _dl_catch_exception (&exception, openaux, &args);
		if (__glibc_unlikely (exception.errstring != NULL))
		  {
		    if (err)
		      errno_reason = err;
		    else
		      errno_reason = -1;
		    goto out;
		  }
		else
		  dep = args.aux;

		if (! dep->l_reserved)
		  {
		    /* Allocate new entry.  */
		    struct list *newp;

		    newp = alloca (sizeof (struct list));

		    /* Append DEP to the list.  */
		    newp->map = dep;
		    newp->done = 0;
		    newp->next = NULL;
		    tail->next = newp;
		    tail = newp;
		    ++nlist;
		    /* Set the mark bit that says it's already in the list.  */
		    dep->l_reserved = 1;
		  }

		/* Remember this dependency.  */
		if (needed != NULL)
		  needed[nneeded++] = dep;
	      }
	    else if (d->d_tag == DT_AUXILIARY || d->d_tag == DT_FILTER)
	      {
		struct list *newp;

		/* Recognize DSTs.  */
		name = expand_dst (l, strtab + d->d_un.d_val,
				   d->d_tag == DT_AUXILIARY);
		/* Store the tag in the argument structure.  */
		args.name = name;

		/* Say that we are about to load an auxiliary library.  */
		if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS,
				      0))
		  _dl_debug_printf ("load auxiliary object=%s"
				    " requested by file=%s\n",
				    name,
				    DSO_FILENAME (l->l_name));

		/* We must be prepared that the addressed shared
		   object is not available.  For filter objects the dependency
		   must be available.  */
		int err = _dl_catch_exception (&exception, openaux, &args);
		if (__glibc_unlikely (exception.errstring != NULL))
		  {
		    if (d->d_tag == DT_AUXILIARY)
		      {
			/* We are not interested in the error message.  */
			_dl_exception_free (&exception);
			/* Simply ignore this error and continue the work.  */
			continue;
		      }
		    else
		      {
			if (err)
			  errno_reason = err;
			else
			  errno_reason = -1;
			goto out;
		      }
		  }

		/* The auxiliary object is actually available.
		   Incorporate the map in all the lists.  */

		/* Allocate new entry.  This always has to be done.  */
		newp = alloca (sizeof (struct list));

		/* We want to insert the new map before the current one,
		   but we have no back links.  So we copy the contents of
		   the current entry over.  Note that ORIG and NEWP now
		   have switched their meanings.  */
		memcpy (newp, orig, sizeof (*newp));

		/* Initialize new entry.  */
		orig->done = 0;
		orig->map = args.aux;

		/* Remember this dependency.  */
		if (needed != NULL)
		  needed[nneeded++] = args.aux;

		/* We must handle two situations here: the map is new,
		   so we must add it in all three lists.  If the map
		   is already known, we have two further possibilities:
		   - if the object is before the current map in the
		   search list, we do nothing.  It is already found
		   early
		   - if the object is after the current one, we must
		   move it just before the current map to make sure
		   the symbols are found early enough
		*/
		if (args.aux->l_reserved)
		  {
		    /* The object is already somewhere in the list.
		       Locate it first.  */
		    struct list *late;

		    /* This object is already in the search list we
		       are building.  Don't add a duplicate pointer.
		       Just added by _dl_map_object.  */
		    for (late = newp; late->next != NULL; late = late->next)
		      if (late->next->map == args.aux)
			break;

		    if (late->next != NULL)
		      {
			/* The object is somewhere behind the current
			   position in the search path.  We have to
			   move it to this earlier position.  */
			orig->next = newp;

			/* Now remove the later entry from the list
			   and adjust the tail pointer.  */
			if (tail == late->next)
			  tail = late;
			late->next = late->next->next;

			/* We must move the object earlier in the chain.  */
			if (args.aux->l_prev != NULL)
			  args.aux->l_prev->l_next = args.aux->l_next;
			if (args.aux->l_next != NULL)
			  args.aux->l_next->l_prev = args.aux->l_prev;

			args.aux->l_prev = newp->map->l_prev;
			newp->map->l_prev = args.aux;
			if (args.aux->l_prev != NULL)
			  args.aux->l_prev->l_next = args.aux;
			args.aux->l_next = newp->map;
		      }
		    else
		      {
			/* The object must be somewhere earlier in the
			   list.  Undo to the current list element what
			   we did above.  */
			memcpy (orig, newp, sizeof (*newp));
			continue;
		      }
		  }
		else
		  {
		    /* This is easy.  We just add the symbol right here.  */
		    orig->next = newp;
		    ++nlist;
		    /* Set the mark bit that says it's already in the list.  */
		    args.aux->l_reserved = 1;

		    /* The only problem is that in the double linked
		       list of all objects we don't have this new
		       object at the correct place.  Correct this here.  */
		    if (args.aux->l_prev)
		      args.aux->l_prev->l_next = args.aux->l_next;
		    if (args.aux->l_next)
		      args.aux->l_next->l_prev = args.aux->l_prev;

		    args.aux->l_prev = newp->map->l_prev;
		    newp->map->l_prev = args.aux;
		    if (args.aux->l_prev != NULL)
		      args.aux->l_prev->l_next = args.aux;
		    args.aux->l_next = newp->map;
		  }

		/* Move the tail pointer if necessary.  */
		if (orig == tail)
		  tail = newp;

		/* Move on the insert point.  */
		orig = newp;
	      }
	}

      /* Terminate the list of dependencies and store the array address.  */
      if (needed != NULL)
	{
	  needed[nneeded++] = NULL;

	  struct link_map **l_initfini = (struct link_map **)
	    malloc ((2 * nneeded + 1) * sizeof needed[0]);
	  if (l_initfini == NULL)
	    {
	      scratch_buffer_free (&needed_space);
	      _dl_signal_error (ENOMEM, map->l_name, NULL,
				N_("cannot allocate dependency list"));
	    }
	  l_initfini[0] = l;
	  memcpy (&l_initfini[1], needed, nneeded * sizeof needed[0]);
	  memcpy (&l_initfini[nneeded + 1], l_initfini,
		  nneeded * sizeof needed[0]);
	  atomic_write_barrier ();
	  l->l_initfini = l_initfini;
	  l->l_free_initfini = 1;
	}

      /* If we have no auxiliary objects just go on to the next map.  */
      if (runp->done)
	do
	  runp = runp->next;
	while (runp != NULL && runp->done);
    }

 out:
  scratch_buffer_free (&needed_space);

  if (errno == 0 && errno_saved != 0)
    __set_errno (errno_saved);

  struct link_map **old_l_initfini = NULL;
  if (map->l_initfini != NULL && map->l_type == lt_loaded)
    {
      /* This object was previously loaded as a dependency and we have
	 a separate l_initfini list.  We don't need it anymore.  */
      assert (map->l_searchlist.r_list == NULL);
      old_l_initfini = map->l_initfini;
    }

  /* Store the search list we built in the object.  It will be used for
     searches in the scope of this object.  */
  struct link_map **l_initfini =
    (struct link_map **) malloc ((2 * nlist + 1)
				 * sizeof (struct link_map *));
  if (l_initfini == NULL)
    _dl_signal_error (ENOMEM, map->l_name, NULL,
		      N_("cannot allocate symbol search list"));


  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
	{
	  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.  */
      runp->map->l_reserved = 0;
    }

  if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_PRELINK, 0) != 0
      && map == GL(dl_ns)[LM_ID_BASE]._ns_loaded)
    {
      /* If we are to compute conflicts, we have to build local scope
	 for each library, not just the ultimate loader.  */
      for (i = 0; i < nlist; ++i)
	{
	  struct link_map *l = map->l_searchlist.r_list[i];
	  unsigned int j, cnt;

	  /* The local scope has been already computed.  */
	  if (l == map
	      || (l->l_local_scope[0]
		  && l->l_local_scope[0]->r_nlist) != 0)
	    continue;

	  if (l->l_info[AUXTAG] || l->l_info[FILTERTAG])
	    {
	      /* As current DT_AUXILIARY/DT_FILTER implementation needs to be
		 rewritten, no need to bother with prelinking the old
		 implementation.  */
	      _dl_signal_error (EINVAL, l->l_name, NULL, N_("\
Filters not supported with LD_TRACE_PRELINKING"));
	    }

	  cnt = _dl_build_local_scope (l_initfini, l);
	  assert (cnt <= nlist);
	  for (j = 0; j < cnt; j++)
	    {
	      l_initfini[j]->l_reserved = 0;
	      if (j && __builtin_expect (l_initfini[j]->l_info[DT_SYMBOLIC]
					 != NULL, 0))
		l->l_symbolic_in_local_scope = true;
	    }

	  l->l_local_scope[0] =
	    (struct r_scope_elem *) malloc (sizeof (struct r_scope_elem)
					    + (cnt
					       * sizeof (struct link_map *)));
	  if (l->l_local_scope[0] == NULL)
	    _dl_signal_error (ENOMEM, map->l_name, NULL,
			      N_("cannot allocate symbol search list"));
	  l->l_local_scope[0]->r_nlist = cnt;
	  l->l_local_scope[0]->r_list =
	    (struct link_map **) (l->l_local_scope[0] + 1);
	  memcpy (l->l_local_scope[0]->r_list, l_initfini,
		  cnt * sizeof (struct link_map *));
	}
    }

  /* Maybe we can remove some relocation dependencies now.  */
  struct link_map_reldeps *l_reldeps = NULL;
  if (map->l_reldeps != NULL)
    {
      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)
	  {
	    /* Need to allocate new array of relocation dependencies.  */
	    l_reldeps = malloc (sizeof (*l_reldeps)
				+ map->l_reldepsmax
				  * sizeof (struct link_map *));
	    if (l_reldeps == NULL)
	      /* Bad luck, keep the reldeps duplicated between
		 map->l_reldeps->list and map->l_initfini lists.  */
	      ;
	    else
	      {
		unsigned int j = i;
		memcpy (&l_reldeps->list[0], &list[0],
			i * sizeof (struct link_map *));
		for (i = i + 1; i < map->l_reldeps->act; ++i)
		  if (!list[i]->l_reserved)
		    l_reldeps->list[j++] = list[i];
		l_reldeps->act = j;
	      }
	  }

      for (i = 0; i < nlist; ++i)
	map->l_searchlist.r_list[i]->l_reserved = 0;
    }

  /* 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 *));

  /* If libc.so.6 is the main map, it participates in the sort, so
     that the relocation order is correct regarding libc.so.6.  */
  _dl_sort_maps (l_initfini, nlist,
		 (l_initfini[0] != GL (dl_ns)[l_initfini[0]->l_ns].libc_map),
		 false);

  /* Terminate the list of dependencies.  */
  l_initfini[nlist] = NULL;
  atomic_write_barrier ();
  map->l_initfini = l_initfini;
  map->l_free_initfini = 1;
  if (l_reldeps != NULL)
    {
      atomic_write_barrier ();
      void *old_l_reldeps = map->l_reldeps;
      map->l_reldeps = l_reldeps;
      _dl_scope_free (old_l_reldeps);
    }
  if (old_l_initfini != NULL)
    _dl_scope_free (old_l_initfini);

  if (errno_reason)
    _dl_signal_exception (errno_reason == -1 ? 0 : errno_reason,
			  &exception, NULL);
}