[Zucchini] Validate equivalences on load

A follow-up to
https://chromium-review.googlesource.com/c/chromium/src/+/1028575

This moves patch_apply logic to check bounds of an equivalences from
the call site of GetNext() to an internal function in the patch_reader.
This means the equivalence consumer can use the equivalences without
checking anything to do with bounds.

I have manually tested that this doesn't appear to break any existing
valid patches and it appears to catch all the same errors change
1028575 fixed so I can safely reverse that change.

BUG: 837096

Change-Id: I84ccd9e1493f32d16eace4dd8e67586f559220d3
Reviewed-on: https://chromium-review.googlesource.com/1028836
Commit-Queue: Calder Kitagawa <ckitagawa@google.com>
Reviewed-by: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#554536}
NOKEYCHECK=True
GitOrigin-RevId: ce5642400b37f5ff2b0a1213522f984bca8a080a

1 files changed, 0 insertions, 13 deletions

diff --git a/zucchini_apply.cc b/zucchini_apply.cc
index 63b8ce0..b67bf63 100644
--- a/zucchini_apply.cc
+++ b/zucchini_apply.cc
@@ -26,13 +26,6 @@ bool ApplyEquivalenceAndExtraData(ConstBufferView old_image,
 
   for (auto equivalence = equiv_source.GetNext(); equivalence.has_value();
        equivalence = equiv_source.GetNext()) {
-    // TODO(ckitagawa): Ensure guards don't overflow. Move these validation
-    // check to the patch reader.
-    // Validate that the |equivalence| is within the |new_image|.
-    if (equivalence->dst_end() > new_image.size()) {
-      LOG(ERROR) << "Out of bounds equivalence";
-      return false;
-    }
     MutableBufferView::iterator next_dst_it =
         new_image.begin() + equivalence->dst_offset;
     CHECK(next_dst_it >= dst_it);
@@ -47,12 +40,6 @@ bool ApplyEquivalenceAndExtraData(ConstBufferView old_image,
     // copy should be valid.
     dst_it = std::copy(extra_data->begin(), extra_data->end(), dst_it);
     CHECK_EQ(dst_it, next_dst_it);
-
-    // Validate that the |equivalence| is within the |old_image|.
-    if (equivalence->src_end() > old_image.size()) {
-      LOG(ERROR) << "Out of bounds equivalence";
-      return false;
-    }
     dst_it = std::copy_n(old_image.begin() + equivalence->src_offset,
                          equivalence->length, dst_it);
     CHECK_EQ(dst_it, next_dst_it + equivalence->length);