Make stack canary value harder to read through read overflow

ChangeLog

@@ -1,5 +1,10 @@
 2011-05-15  Ulrich Drepper  <drepper@gmail.com>
 
+	[BZ #10149]
+	* sysdeps/unix/sysv/linux/dl-osinfo.h (_dl_setup_stack_chk_guard):
+	First byte (not low byte) is now always NUL.
+	* sysdeps/generic/dl-osinfo.h (_dl_setup_stack_chk_guard): Likewise.
+
 	* sysdeps/unix/sysv/linux/dl-osinfo.h (_dl_setup_stack_chk_guard):
 	Use non-cancelable interfaces.
 

NEWS

@@ -9,12 +9,13 @@ Version 2.14
 
 * The following bugs are resolved with this release:
 
-  386, 9809, 11257, 11258, 11487, 11532, 11578, 11653, 11668, 11724, 11901,
+  386, 9809, 10149, 11257, 11258, 11487, 11532, 11578, 11653, 11668, 11724,
-  11945, 11947, 11952, 12052, 12083, 12158, 12178, 12200, 12346, 12393,
+  11901, 11945, 11947, 11952, 12052, 12083, 12158, 12178, 12200, 12346,
-  12420, 12432, 12445, 12449, 12453, 12454, 12460, 12469, 12489, 12509,
+  12393, 12420, 12432, 12445, 12449, 12453, 12454, 12460, 12469, 12489,
-  12510, 12511, 12518, 12527, 12541, 12545, 12551, 12582, 12583, 12587,
+  12509, 12510, 12511, 12518, 12527, 12541, 12545, 12551, 12582, 12583,
-  12597, 12601, 12611, 12625, 12626, 12631, 12650, 12653, 12655, 12660,
+  12587, 12597, 12601, 12611, 12625, 12626, 12631, 12650, 12653, 12655,
-  12681, 12685, 12711, 12713, 12714, 12717, 12723, 12724, 12734, 12738
+  12660, 12681, 12685, 12711, 12713, 12714, 12717, 12723, 12724, 12734,
+  12738
 
 * The RPC implementation in libc is obsoleted.  Old programs keep working
   but new programs cannot be linked with the routines in libc anymore.

sysdeps/generic/dl-osinfo.h

@@ -1,5 +1,5 @@
 /* Operating system specific code for generic dynamic loader functions.
-   Copyright (C) 2009 Free Software Foundation, Inc.
+   Copyright (C) 2009, 2011 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
@@ -17,23 +17,35 @@
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */
 
+#include <endian.h>
 #include <stdint.h>
 
 static inline uintptr_t __attribute__ ((always_inline))
 _dl_setup_stack_chk_guard (void *dl_random)
 {
-  uintptr_t ret;
+  union
+  {
+    uintptr_t num;
+    unsigned char bytes[sizeof (uintptr_t)];
+  } ret = { 0 };
+
   if (dl_random == NULL)
     {
-      ret = 0;
+      ret.bytes[sizeof (ret) - 2] = 255;
-      unsigned char *p = (unsigned char *) &ret;
+      ret.bytes[sizeof (ret) - 3] = '\n';
-      p[sizeof (ret) - 1] = 255;
-      p[sizeof (ret) - 2] = '\n';
-      p[0] = 0;
     }
   else
-    memcpy (&ret, dl_random, sizeof (ret));
+    {
-  return ret;
+      memcpy (ret.bytes, dl_random, sizeof (ret));
+#if BYTE_ORDER == LITTLE_ENDIAN
+      ret.num &= ~0xff;
+#elif BYTE_ORDER == BIG_ENDIAN
+      ret.num &= ~(0xff << (8 * (sizeof (ret) - 1)));
+#else
+# error "BYTE_ORDER unknown"
+#endif
+    }
+  return ret.num;
 }
 
 static inline uintptr_t __attribute__ ((always_inline))

sysdeps/unix/sysv/linux/dl-osinfo.h

@@ -19,6 +19,7 @@
 
 #include <kernel-features.h>
 #include <dl-sysdep.h>
+#include <endian.h>
 #include <fcntl.h>
 #include <stdint.h>
 #include <not-cancel.h>
@@ -63,32 +64,46 @@ dl_fatal (const char *str)
 static inline uintptr_t __attribute__ ((always_inline))
 _dl_setup_stack_chk_guard (void *dl_random)
 {
-  uintptr_t ret;
+  union
+  {
+    uintptr_t num;
+    unsigned char bytes[sizeof (uintptr_t)];
+  } ret;
+
 #ifndef __ASSUME_AT_RANDOM
   if (__builtin_expect (dl_random == NULL, 0))
     {
+      const size_t filllen = sizeof (ret.bytes) - 1;
+      ret.num = 0;
 # ifdef ENABLE_STACKGUARD_RANDOMIZE
       int fd = open_not_cancel_2 ("/dev/urandom", O_RDONLY);
       if (fd >= 0)
 	{
-	  ssize_t reslen = read_not_cancel (fd, &ret, sizeof (ret));
+	  ssize_t reslen = read_not_cancel (fd, ret.bytes + 1, filllen);
 	  close_not_cancel_no_status (fd);
-	  if (reslen == (ssize_t) sizeof (ret))
+	  if (reslen == (ssize_) filllen)
-	    return ret;
+	    return ret.num;
 	}
 # endif
-      ret = 0;
+      ret.bytes[filllen - 2] = 255;
-      unsigned char *p = (unsigned char *) &ret;
+      ret.bytes[filllen - 3] = '\n';
-      p[sizeof (ret) - 1] = 255;
-      p[sizeof (ret) - 2] = '\n';
     }
   else
 #endif
-    /* We need in the moment only 8 bytes on 32-bit platforms and 16
+    {
-       bytes on 64-bit platforms.  Therefore we can use the data
+      /* We need in the moment only 8 bytes on 32-bit platforms and 16
-       directly and not use the kernel-provided data to seed a PRNG.  */
+	 bytes on 64-bit platforms.  Therefore we can use the data
-    memcpy (&ret, dl_random, sizeof (ret));
+	 directly and not use the kernel-provided data to seed a PRNG.  */
-  return ret;
+      memcpy (ret.bytes, dl_random, sizeof (ret));
+#if BYTE_ORDER == LITTLE_ENDIAN
+      ret.num &= ~0xff;
+#elif BYTE_ORDER == BIG_ENDIAN
+      ret.num &= ~(0xff << (8 * (sizeof (ret) - 1)));
+#else
+# error "BYTE_ORDER unknown"
+#endif
+    }
+  return ret.num;
 }
 
 static inline uintptr_t __attribute__ ((always_inline))