Merge lp:~brandontschaefer/miral/fix-unsigned-to-long-overflow into lp:miral

[Brandon Schaefer]

On armhf where sizeof(long) == sizeof(int) an overflow was happening when casting the unsigned::max() aspect to a long resulting in a -1. This allows for a div by 0 because the error check is positive due to the overflow:

On armhf where sizeof(long) == sizeof(int) an overflow was happening when casting the unsigned::max() aspect to a long resulting in a -1. This allows for a div by 0 because the error check is positive due to the overflow:

error = 640 * 0 - 420 * -1

if (error > 0)
  // ends up in div by 0

The fix here sets the max value from unsigned::max() to int::max() since sizeof(long) >= sizeof(int). So an unsigned int can be casted into a long with out overflow.

[Mir CI Bot (mir-ci-bot)]

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review: Needs Fixing (continuous-integration)

[Brandon Schaefer (brandontschaefer)]

Better fix:
https://code.launchpad.net/~alan-griffiths/miral/fix-1717061/+merge/330832

Unmerged revisions

580. By Brandon Schaefer on 2017-09-14

* Set the min_aspect height and max_aspect width as an int::max().
  Due to the aspects being cast into a long, we dont want to overflow
  on a 32bit arch. sizeof(long) >= sizeof(int)

=== modified file 'miral/window_info.cpp'
--- miral/window_info.cpp	2017-08-10 16:59:22 +0000
+++ miral/window_info.cpp	2017-09-14 21:22:30 +0000
@@ -79,8 +79,9 @@
     confine_pointer(optional_value_or_default(params.confine_pointer(), mir_pointer_unconfined)),
     width_inc{optional_value_or_default(params.width_inc(), DeltaX{1})},
     height_inc{optional_value_or_default(params.height_inc(), DeltaY{1})},
-    min_aspect(optional_value_or_default(params.min_aspect(), AspectRatio{0U, std::numeric_limits<unsigned>::max()})),
-    max_aspect(optional_value_or_default(params.max_aspect(), AspectRatio{std::numeric_limits<unsigned>::max(), 0U})),
+    // sizeof(long) >= sizeof(int). We cast from unsigned to long so we need to fit within a signed int without overflowing
+    min_aspect(optional_value_or_default(params.min_aspect(), AspectRatio{0U, std::numeric_limits<int>::max()})),
+    max_aspect(optional_value_or_default(params.max_aspect(), AspectRatio{std::numeric_limits<int>::max(), 0U})),
     shell_chrome(optional_value_or_default(params.shell_chrome(), mir_shell_chrome_normal))
 {
     if (params.output_id().is_set())