Don't use gigs of memory with invalid palette sizes

PIL/BmpImagePlugin.py

@@ -129,6 +129,8 @@ class BmpImageFile(ImageFile.ImageFile):
             greyscale = 1
             if colors == 2:
                 indices = (0, 255)
+            elif colors > 2**16 or colors <=0: #We're reading a i32. 
+                raise IOError("Unsupported BMP Palette size (%d)" % colors)
             else:
                 indices = list(range(colors))
             for i in indices:

Tests/bmpsuite.py

@@ -0,0 +1,25 @@
+from tester import *
+
+from PIL import Image
+import os
+
+base = 'Tests/images/bmp/'
+
+
+def get_files(d, ext='.bmp'):
+    return [os.path.join(base,d,f) for f
+            in os.listdir(os.path.join(base, d)) if ext in f]
+
+def test_bad():
+    """ These shouldn't crash, but they shouldn't return anything either """
+    for f in get_files('b'):
+        try:
+            print ("Trying %s"%f)
+            im = Image.open(f)
+            print ("%s, %s" %(im.size, im.mode))
+            im.load()
+        except Exception as msg:
+            print ("Bad Image %s: %s" %(f,msg))
+
+            
+