Return nullptr when ReadBuffer becomes invalid

This especially helps in SkDrawLooper because we can bail out early
instead of looping for a potentially long time, e.g. when fuzzed
input says count is a large number.

This also cleans up validate in a few spots, and adds validateCanReadN
as a helper function.

Bug: skia:7937
Change-Id: Ic5eff357c8cadc91eeafc6e39c78c570ba74df2f
Reviewed-on: https://skia-review.googlesource.com/128847
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/core/SkPictureData.cpp b/src/core/SkPictureData.cpp
index 571c6d7b35..efd41837d9 100644
--- a/src/core/SkPictureData.cpp
+++ b/src/core/SkPictureData.cpp
@@ -427,7 +427,7 @@ void SkPictureData::parseBufferTag(SkReadBuffer& buffer, uint32_t tag, uint32_t
         case SK_PICT_READER_TAG: {
             // Preflight check that we can initialize all data from the buffer
             // before allocating it.
-            if (!buffer.validate(size <= buffer.available())) {
+            if (!buffer.validateCanReadN<uint8_t>(size)) {
                 return;
             }
             auto data(SkData::MakeUninitialized(size));