Avoid late dlopen failure due to scope, TLS slotinfo updates [BZ #25112]

This change splits the scope and TLS slotinfo updates in dlopen into
two parts: one to resize the data structures, and one to actually apply
the update.  The call to add_to_global_resize in dl_open_worker is moved
before the demarcation point at which no further memory allocations are
allowed.

_dl_add_to_slotinfo is adjusted to make the list update optional.  There
is some optimization possibility here because we could grow the slotinfo
list of arrays in a single call, one the largest TLS modid is known.

This commit does not fix the fatal meory allocation failure in
_dl_update_slotinfo.  Ideally, this error during dlopen should be
recoverable.

The update order of scopes and TLS data structures is retained, although
it appears to be more correct to fully initialize TLS first, and then
expose symbols in the newly loaded objects via the scope update.

Tested on x86_64-linux-gnu.

Change-Id: I240c58387dabda3ca1bcab48b02115175fa83d6c

1 files changed, 241 insertions, 124 deletions

diff --git a/elf/dl-open.c b/elf/dl-open.c
index bedbd3a..03aaff7 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -33,6 +33,7 @@
 #include <stap-probe.h>
 #include <atomic.h>
 #include <libc-internal.h>
+#include <array_length.h>
 
 #include <dl-dst.h>
 #include <dl-prop.h>
@@ -214,6 +215,215 @@ _dl_find_dso_for_object (const ElfW(Addr) addr)
 }
 rtld_hidden_def (_dl_find_dso_for_object);
 
+/* Return true if NEW is found in the scope for MAP.  */
+static size_t
+scope_has_map (struct link_map *map, struct link_map *new)
+{
+  size_t cnt;
+  for (cnt = 0; map->l_scope[cnt] != NULL; ++cnt)
+    if (map->l_scope[cnt] == &new->l_searchlist)
+      return true;
+  return false;
+}
+
+/* Return the length of the scope for MAP.  */
+static size_t
+scope_size (struct link_map *map)
+{
+  size_t cnt;
+  for (cnt = 0; map->l_scope[cnt] != NULL; )
+    ++cnt;
+  return cnt;
+}
+
+/* Resize the scopes of depended-upon objects, so that the new object
+   can be added later without further allocation of memory.  This
+   function can raise an exceptions due to malloc failure.  */
+static void
+resize_scopes (struct link_map *new)
+{
+  /* If the file is not loaded now as a dependency, add the search
+     list of the newly loaded object to the scope.  */
+  for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
+    {
+      struct link_map *imap = new->l_searchlist.r_list[i];
+
+      /* If the initializer has been called already, the object has
+	 not been loaded here and now.  */
+      if (imap->l_init_called && imap->l_type == lt_loaded)
+	{
+	  if (scope_has_map (imap, new))
+	    /* Avoid duplicates.  */
+	    continue;
+
+	  size_t cnt = scope_size (imap);
+	  if (__glibc_unlikely (cnt + 1 >= imap->l_scope_max))
+	    {
+	      /* The l_scope array is too small.  Allocate a new one
+		 dynamically.  */
+	      size_t new_size;
+	      struct r_scope_elem **newp;
+
+	      if (imap->l_scope != imap->l_scope_mem
+		  && imap->l_scope_max < array_length (imap->l_scope_mem))
+		{
+		  /* If the current l_scope memory is not pointing to
+		     the static memory in the structure, but the
+		     static memory in the structure is large enough to
+		     use for cnt + 1 scope entries, then switch to
+		     using the static memory.  */
+		  new_size = array_length (imap->l_scope_mem);
+		  newp = imap->l_scope_mem;
+		}
+	      else
+		{
+		  new_size = imap->l_scope_max * 2;
+		  newp = (struct r_scope_elem **)
+		    malloc (new_size * sizeof (struct r_scope_elem *));
+		  if (newp == NULL)
+		    _dl_signal_error (ENOMEM, "dlopen", NULL,
+				      N_("cannot create scope list"));
+		}
+
+	      /* Copy the array and the terminating NULL.  */
+	      memcpy (newp, imap->l_scope,
+		      (cnt + 1) * sizeof (imap->l_scope[0]));
+	      struct r_scope_elem **old = imap->l_scope;
+
+	      imap->l_scope = newp;
+
+	      if (old != imap->l_scope_mem)
+		_dl_scope_free (old);
+
+	      imap->l_scope_max = new_size;
+	    }
+	}
+    }
+}
+
+/* Second stage of resize_scopes: Add NEW to the scopes.  Also print
+   debugging information about scopes if requested.
+
+   This function cannot raise an exception because all required memory
+   has been allocated by a previous call to resize_scopes.  */
+static void
+update_scopes (struct link_map *new)
+{
+  for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
+    {
+      struct link_map *imap = new->l_searchlist.r_list[i];
+      int from_scope = 0;
+
+      if (imap->l_init_called && imap->l_type == lt_loaded)
+	{
+	  if (scope_has_map (imap, new))
+	    /* Avoid duplicates.  */
+	    continue;
+
+	  size_t cnt = scope_size (imap);
+	  /* Assert that resize_scopes has sufficiently enlarged the
+	     array.  */
+	  assert (cnt + 1 < imap->l_scope_max);
+
+	  /* First terminate the extended list.  Otherwise a thread
+	     might use the new last element and then use the garbage
+	     at offset IDX+1.  */
+	  imap->l_scope[cnt + 1] = NULL;
+	  atomic_write_barrier ();
+	  imap->l_scope[cnt] = &new->l_searchlist;
+
+	  from_scope = cnt;
+	}
+
+      /* Print scope information.  */
+      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_SCOPES))
+	_dl_show_scope (imap, from_scope);
+    }
+}
+
+/* Call _dl_add_to_slotinfo with DO_ADD set to false, to allocate
+   space in GL (dl_tls_dtv_slotinfo_list).  This can raise an
+   exception.  The return value is true if any of the new objects use
+   TLS.  */
+static bool
+resize_tls_slotinfo (struct link_map *new)
+{
+  bool any_tls = false;
+  for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
+    {
+      struct link_map *imap = new->l_searchlist.r_list[i];
+
+      /* Only add TLS memory if this object is loaded now and
+	 therefore is not yet initialized.  */
+      if (! imap->l_init_called && imap->l_tls_blocksize > 0)
+	{
+	  _dl_add_to_slotinfo (imap, false);
+	  any_tls = true;
+	}
+    }
+  return any_tls;
+}
+
+/* Second stage of TLS update, after resize_tls_slotinfo.  This
+   function does not raise any exception.  It should only be called if
+   resize_tls_slotinfo returned true.  */
+static void
+update_tls_slotinfo (struct link_map *new)
+{
+  unsigned int first_static_tls = new->l_searchlist.r_nlist;
+  for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
+    {
+      struct link_map *imap = new->l_searchlist.r_list[i];
+
+      /* Only add TLS memory if this object is loaded now and
+	 therefore is not yet initialized.  */
+      if (! imap->l_init_called && imap->l_tls_blocksize > 0)
+	{
+	  _dl_add_to_slotinfo (imap, true);
+
+	  if (imap->l_need_tls_init
+	      && first_static_tls == new->l_searchlist.r_nlist)
+	    first_static_tls = i;
+	}
+    }
+
+  if (__builtin_expect (++GL(dl_tls_generation) == 0, 0))
+    _dl_fatal_printf (N_("\
+TLS generation counter wrapped!  Please report this."));
+
+  /* We need a second pass for static tls data, because
+     _dl_update_slotinfo must not be run while calls to
+     _dl_add_to_slotinfo are still pending.  */
+  for (unsigned int i = first_static_tls; i < new->l_searchlist.r_nlist; ++i)
+    {
+      struct link_map *imap = new->l_searchlist.r_list[i];
+
+      if (imap->l_need_tls_init
+	  && ! imap->l_init_called
+	  && imap->l_tls_blocksize > 0)
+	{
+	  /* For static TLS we have to allocate the memory here and
+	     now, but we can delay updating the DTV.  */
+	  imap->l_need_tls_init = 0;
+#ifdef SHARED
+	  /* Update the slot information data for at least the
+	     generation of the DSO we are allocating data for.  */
+
+	  /* FIXME: This can terminate the process on memory
+	     allocation failure.  It is not possible to raise
+	     exceptions from this context; to fix this bug,
+	     _dl_update_slotinfo would have to be split into two
+	     operations, similar to resize_scopes and update_scopes
+	     above.  This is related to bug 16134.  */
+	  _dl_update_slotinfo (imap->l_tls_modid);
+#endif
+
+	  GL(dl_init_static_tls) (imap);
+	  assert (imap->l_need_tls_init == 0);
+	}
+    }
+}
+
 /* struct dl_init_args and call_dl_init are used to call _dl_init with
    exception handling disabled.  */
 struct dl_init_args
@@ -434,133 +644,40 @@ dl_open_worker (void *a)
      relocation.  */
   _dl_open_check (new);
 
-  /* If the file is not loaded now as a dependency, add the search
-     list of the newly loaded object to the scope.  */
-  bool any_tls = false;
-  unsigned int first_static_tls = new->l_searchlist.r_nlist;
-  for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
-    {
-      struct link_map *imap = new->l_searchlist.r_list[i];
-      int from_scope = 0;
+  /* This only performs the memory allocations.  The actual update of
+     the scopes happens below, after failure is impossible.  */
+  resize_scopes (new);
 
-      /* If the initializer has been called already, the object has
-	 not been loaded here and now.  */
-      if (imap->l_init_called && imap->l_type == lt_loaded)
-	{
-	  struct r_scope_elem **runp = imap->l_scope;
-	  size_t cnt = 0;
-
-	  while (*runp != NULL)
-	    {
-	      if (*runp == &new->l_searchlist)
-		break;
-	      ++cnt;
-	      ++runp;
-	    }
-
-	  if (*runp != NULL)
-	    /* Avoid duplicates.  */
-	    continue;
-
-	  if (__glibc_unlikely (cnt + 1 >= imap->l_scope_max))
-	    {
-	      /* The 'r_scope' array is too small.  Allocate a new one
-		 dynamically.  */
-	      size_t new_size;
-	      struct r_scope_elem **newp;
-
-#define SCOPE_ELEMS(imap) \
-  (sizeof (imap->l_scope_mem) / sizeof (imap->l_scope_mem[0]))
+  /* Increase the size of the GL (dl_tls_dtv_slotinfo_list) data
+     structure.  */
+  bool any_tls = resize_tls_slotinfo (new);
 
-	      if (imap->l_scope != imap->l_scope_mem
-		  && imap->l_scope_max < SCOPE_ELEMS (imap))
-		{
-		  new_size = SCOPE_ELEMS (imap);
-		  newp = imap->l_scope_mem;
-		}
-	      else
-		{
-		  new_size = imap->l_scope_max * 2;
-		  newp = (struct r_scope_elem **)
-		    malloc (new_size * sizeof (struct r_scope_elem *));
-		  if (newp == NULL)
-		    _dl_signal_error (ENOMEM, "dlopen", NULL,
-				      N_("cannot create scope list"));
-		}
-
-	      memcpy (newp, imap->l_scope, cnt * sizeof (imap->l_scope[0]));
-	      struct r_scope_elem **old = imap->l_scope;
-
-	      imap->l_scope = newp;
-
-	      if (old != imap->l_scope_mem)
-		_dl_scope_free (old);
-
-	      imap->l_scope_max = new_size;
-	    }
-
-	  /* First terminate the extended list.  Otherwise a thread
-	     might use the new last element and then use the garbage
-	     at offset IDX+1.  */
-	  imap->l_scope[cnt + 1] = NULL;
-	  atomic_write_barrier ();
-	  imap->l_scope[cnt] = &new->l_searchlist;
-
-	  /* Print only new scope information.  */
-	  from_scope = cnt;
-	}
-      /* Only add TLS memory if this object is loaded now and
-	 therefore is not yet initialized.  */
-      else if (! imap->l_init_called
-	       /* Only if the module defines thread local data.  */
-	       && __builtin_expect (imap->l_tls_blocksize > 0, 0))
-	{
-	  /* Now that we know the object is loaded successfully add
-	     modules containing TLS data to the slot info table.  We
-	     might have to increase its size.  */
-	  _dl_add_to_slotinfo (imap);
-
-	  if (imap->l_need_tls_init
-	      && first_static_tls == new->l_searchlist.r_nlist)
-	    first_static_tls = i;
-
-	  /* We have to bump the generation counter.  */
-	  any_tls = true;
-	}
-
-      /* Print scope information.  */
-      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_SCOPES))
-	_dl_show_scope (imap, from_scope);
-    }
-
-  /* Bump the generation number if necessary.  */
-  if (any_tls && __builtin_expect (++GL(dl_tls_generation) == 0, 0))
-    _dl_fatal_printf (N_("\
-TLS generation counter wrapped!  Please report this."));
-
-  /* We need a second pass for static tls data, because _dl_update_slotinfo
-     must not be run while calls to _dl_add_to_slotinfo are still pending.  */
-  for (unsigned int i = first_static_tls; i < new->l_searchlist.r_nlist; ++i)
-    {
-      struct link_map *imap = new->l_searchlist.r_list[i];
-
-      if (imap->l_need_tls_init
-	  && ! imap->l_init_called
-	  && imap->l_tls_blocksize > 0)
-	{
-	  /* For static TLS we have to allocate the memory here and
-	     now, but we can delay updating the DTV.  */
-	  imap->l_need_tls_init = 0;
-#ifdef SHARED
-	  /* Update the slot information data for at least the
-	     generation of the DSO we are allocating data for.  */
-	  _dl_update_slotinfo (imap->l_tls_modid);
-#endif
+  /* Perform the necessary allocations for adding new global objects
+     to the global scope below.  */
+  if (mode & RTLD_GLOBAL)
+    add_to_global_resize (new);
 
-	  GL(dl_init_static_tls) (imap);
-	  assert (imap->l_need_tls_init == 0);
-	}
-    }
+  /* Demarcation point: After this, no recoverable errors are allowed.
+     All memory allocations for new objects must have happened
+     before.  */
+
+  /* Second stage after resize_scopes: Actually perform the scope
+     update.  After this, dlsym and lazy binding can bind to new
+     objects.  */
+  update_scopes (new);
+
+  /* FIXME: It is unclear whether the order here is correct.
+     Shouldn't new objects be made available for binding (and thus
+     execution) only after there TLS data has been set up fully?
+     Fixing bug 16134 will likely make this distinction less
+     important.  */
+
+  /* Second stage after resize_tls_slotinfo: Update the slotinfo data
+     structures.  */
+  if (any_tls)
+    /* FIXME: This calls _dl_update_slotinfo, which aborts the process
+       on memory allocation failure.  See bug 16134.  */
+    update_tls_slotinfo (new);
 
   /* Notify the debugger all new objects have been relocated.  */
   if (relocation_in_progress)