[babl] babl_format_new(): fix global-buffer-overflow

[Øyvind Kolås <ok src gnome org>]

commit df222a5a96cb92c518428474b03dbe8c05af6bd2
Author: Roman Lebedev <lebedev ri gmail com>
Date:   Sat Jun 13 16:59:35 2015 +0300

    babl_format_new(): fix global-buffer-overflow
    
    If we pass a string into this function, and this string is shorter than
    sizeof(Babl), macro BABL_IS_BABL() will read past string bounds,
    and bad things may happen.
    
    NOTE: if a string will be passed into this function, that is not
    handled by those  if (!strcmp (arg, "<...>")),  global-buffer-overflow
    will still happen. i am not sure if/what can be done about it :(
    
    Fixes following error:
    =================================================================
    ==1657==ERROR: AddressSanitizer: global-buffer-overflow on address 0x7fd3026d6c20 at pc 0x7fd3026b6e4a bp 
0x7fffaac308a0 sp 0x7fffaac30898
    READ of size 4 at 0x7fd3026d6c20 thread T0
        0 0x7fd3026b6e49 in babl_format_new /home/lebedevri/src/_GIMP/babl/babl/babl-format.c:317
        1 0x7fd3026bf44f in construct_double_format /home/lebedevri/src/_GIMP/babl/babl/babl-model.c:259
        2 0x7fd3026bfd12 in babl_model_new /home/lebedevri/src/_GIMP/babl/babl/babl-model.c:204
        3 0x7fd3026acce5 in babl_core_init /home/lebedevri/src/_GIMP/babl/babl/babl-core.c:128
        4 0x7fd3026a9379 in babl_init /home/lebedevri/src/_GIMP/babl/babl/babl.c:145
        5 0x7fd306e5a3d1 in gegl_post_parse_hook (/usr/local/lib/libgegl-0.3.so.0+0x523d1)
        6 0x7fd301f5d238 in g_option_context_parse (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x55238)
        7 0x7fd301f5e193 in g_option_context_parse_strv (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x56193)
        8 0x48b8cf in main (/usr/local/bin/gimp-2.9+0x48b8cf)
        9 0x7fd300f71b44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b44)
        10 0x486b68 (/usr/local/bin/gimp-2.9+0x486b68)
    
    0x7fd3026d6c23 is located 0 bytes to the right of global variable '*.LC8' from 'babl-model.c' 
(0x7fd3026d6c20) of size 3
      '*.LC8' is ascii string 'id'
    SUMMARY: AddressSanitizer: global-buffer-overflow /home/lebedevri/src/_GIMP/babl/babl/babl-format.c:317 
babl_format_new
    Shadow bytes around the buggy address:
      0x0ffae04d2d70: f9 f9 f9 f9 00 00 04 f9 f9 f9 f9 f9 00 00 02 f9
    =>0x0ffae04d2d80: f9 f9 f9 f9[03]f9 f9 f9 f9 f9 f9 f9 00 02 f9 f9
      0x0ffae04d2d90: f9 f9 f9 f9 05 f9 f9 f9 f9 f9 f9 f9 00 00 00 00
    Shadow byte legend (one shadow byte represents 8 application bytes):
      Addressable:           00
      Partially addressable: 01 02 03 04 05 06 07
      Heap left redzone:       fa
      Heap right redzone:      fb
      Freed heap region:       fd
      Stack left redzone:      f1
      Stack mid redzone:       f2
      Stack right redzone:     f3
      Stack partial redzone:   f4
      Stack after return:      f5
      Stack use after scope:   f8
      Global redzone:          f9
      Global init order:       f6
      Poisoned by user:        f7
      Contiguous container OOB:fc
      ASan internal:           fe
    ==1657==ABORTING

 babl/babl-format.c |   44 +++++++++++++++++++++++---------------------
 1 files changed, 23 insertions(+), 21 deletions(-)
---
diff --git a/babl/babl-format.c b/babl/babl-format.c
index 757ae58..60a916e 100644
--- a/babl/babl-format.c
+++ b/babl/babl-format.c
@@ -314,7 +314,29 @@ babl_format_new (const void *first_arg,
 
   while (1)
     {
-      if (BABL_IS_BABL (arg))
+      /* first, we assume arguments to be strings */
+      if (!strcmp (arg, "id"))
+        {
+          id = va_arg (varg, int);
+        }
+
+      else if (!strcmp (arg, "name"))
+        {
+          name = babl_strdup (va_arg (varg, char *));
+        }
+
+      else if (!strcmp (arg, "packed"))
+        {
+          planar = 0;
+        }
+
+      else if (!strcmp (arg, "planar"))
+        {
+          planar = 1;
+        }
+
+      /* if we didn't point to a known string, we assume argument to be babl */
+      else if (BABL_IS_BABL (arg))
         {
           Babl *babl = (Babl *) arg;
 
@@ -377,26 +399,6 @@ babl_format_new (const void *first_arg,
                 break;
             }
         }
-      /* if we didn't point to a babl, we assume arguments to be strings */
-      else if (!strcmp (arg, "id"))
-        {
-          id = va_arg (varg, int);
-        }
-
-      else if (!strcmp (arg, "name"))
-        {
-          name = babl_strdup (va_arg (varg, char *));
-        }
-
-      else if (!strcmp (arg, "packed"))
-        {
-          planar = 0;
-        }
-
-      else if (!strcmp (arg, "planar"))
-        {
-          planar = 1;
-        }
 
       else
         {