[PATCH] elf: Compute correct array size in _dl_init_paths [BZ #22606]

[fweimer at redhat dot com (Florian Weimer)]

2017-12-14  Florian Weimer  <fweimer@redhat.com>

	[BZ #22606]
	CVE-2017-1000408
	* elf/dl-load.c (system_dirs): Update comment.
	(nsystem_dirs_len): Use array_length.
	(_dl_init_paths): Use nsystem_dirs_len to compute the array size.

diff --git a/NEWS b/NEWS
index abbe561dcb..eef51b65a6 100644
--- a/NEWS
+++ b/NEWS
@@ -125,6 +125,11 @@ Security related changes:
   instead of NULL.  This was a regression introduced with the new malloc
   thread cache in glibc 2.26.  Reported by Iain Buclaw.
 
+  CVE-2017-1000408: Incorrect array size computation in _dl_init_paths leads
+  to the allocation of too much memory.  (This is not a security bug per se,
+  it is mentioned here only because of the CVE assignment.)  Reported by
+  Qualys.
+
 The following bugs are resolved with this release:
 
   [The release manager will add the list generated by
diff --git a/elf/dl-load.c b/elf/dl-load.c
index 10d859bd35..82c9f46050 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -37,6 +37,7 @@
 #include <sysdep.h>
 #include <stap-probe.h>
 #include <libc-pointer-arith.h>
+#include <array_length.h>
 
 #include <dl-dst.h>
 #include <dl-load.h>
@@ -103,7 +104,9 @@ static size_t ncapstr attribute_relro;
 static size_t max_capstrlen attribute_relro;
 
 
-/* Get the generated information about the trusted directories.  */
+/* Get the generated information about the trusted directories.  Use
+   an array of concatenated strings to avoid relocations.  See
+   gen-trusted-dirs.awk.  */
 #include "trusted-dirs.h"
 
 static const char system_dirs[] = SYSTEM_DIRS;
@@ -111,9 +114,7 @@ static const size_t system_dirs_len[] =
 {
   SYSTEM_DIRS_LEN
 };
-#define nsystem_dirs_len \
-  (sizeof (system_dirs_len) / sizeof (system_dirs_len[0]))
-
+#define nsystem_dirs_len array_length (system_dirs_len)
 
 static bool
 is_trusted_path (const char *path, size_t len)
@@ -685,9 +686,8 @@ _dl_init_paths (const char *llp)
 		 + ncapstr * sizeof (enum r_dir_status))
 		/ sizeof (struct r_search_path_elem));
 
-  rtld_search_dirs.dirs[0] = (struct r_search_path_elem *)
-    malloc ((sizeof (system_dirs) / sizeof (system_dirs[0]))
-	    * round_size * sizeof (struct r_search_path_elem));
+  rtld_search_dirs.dirs[0] = malloc (nsystem_dirs_len * round_size
+				     * sizeof (struct r_search_path_elem));
   if (rtld_search_dirs.dirs[0] == NULL)
     {
       errstring = N_("cannot create cache for search path");