[PATCH] _dl_map_object_deps: Use struct scratch_buffer [BZ #18023]

[fweimer at redhat dot com (Florian Weimer)]

The function comment suggests that _dl_map_object_deps cannot use
malloc, but it already allocates the l_initfini array on the heap, so
the additional allocation should be acceptable.

2018-06-26  Florian Weimer  <fweimer@redhat.com>

	[BZ #18023]
	* elf/dl-deps.c (_dl_map_object_deps): Use struct
	scratch_buffer instead of extend_alloca.

diff --git a/elf/dl-deps.c b/elf/dl-deps.c
index 20b8e94f2e..9d9b1ba7f2 100644
--- a/elf/dl-deps.c
+++ b/elf/dl-deps.c
@@ -27,6 +27,7 @@
 #include <unistd.h>
 #include <sys/param.h>
 #include <ldsodefs.h>
+#include <scratch_buffer.h>
 
 #include <dl-dst.h>
 
@@ -181,9 +182,8 @@ _dl_map_object_deps (struct link_map *map,
   /* Pointer to last unique object.  */
   tail = &known[nlist - 1];
 
-  /* No alloca'd space yet.  */
-  struct link_map **needed_space = NULL;
-  size_t needed_space_bytes = 0;
+  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
@@ -213,13 +213,12 @@ _dl_map_object_deps (struct link_map *map,
       if (l->l_searchlist.r_list == NULL && l->l_initfini == NULL
 	  && l != map && l->l_ldnum > 0)
 	{
-	  size_t new_size = l->l_ldnum * sizeof (struct link_map *);
-
-	  if (new_size > needed_space_bytes)
-	    needed_space
-	      = extend_alloca (needed_space, needed_space_bytes, new_size);
-
-	  needed = needed_space;
+	  /* 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])
@@ -438,8 +437,11 @@ _dl_map_object_deps (struct link_map *map,
 	  struct link_map **l_initfini = (struct link_map **)
 	    malloc ((2 * nneeded + 1) * sizeof needed[0]);
 	  if (l_initfini == NULL)
-	    _dl_signal_error (ENOMEM, map->l_name, NULL,
-			      N_("cannot allocate dependency list"));
+	    {
+	      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,
@@ -457,6 +459,8 @@ _dl_map_object_deps (struct link_map *map,
     }
 
  out:
+  scratch_buffer_free (&needed_space);
+
   if (errno == 0 && errno_saved != 0)
     __set_errno (errno_saved);