2 files changed, 18 insertions, 16 deletions

diff --git a/gfx/ots/src/ots.h b/gfx/ots/src/ots.h
index 434e068d48..7e3625c737 100644
--- a/gfx/ots/src/ots.h
+++ b/gfx/ots/src/ots.h
@@ -87,8 +87,7 @@ class Buffer {
     if (n_bytes > 1024 * 1024 * 1024) {
       return OTS_FAILURE();
     }
-    if ((offset_ + n_bytes > length_) ||
-        (offset_ > length_ - n_bytes)) {
+    if (length_ < n_bytes || offset_ > length_ - n_bytes) {
       return OTS_FAILURE();
     }
     if (buf) {
@@ -99,7 +98,7 @@ class Buffer {
   }
 
   inline bool ReadU8(uint8_t *value) {
-    if (offset_ + 1 > length_) {
+    if (length_ < 1 || offset_ > length_ - 1) {
       return OTS_FAILURE();
     }
     *value = buffer_[offset_];
@@ -108,7 +107,7 @@ class Buffer {
   }
 
   bool ReadU16(uint16_t *value) {
-    if (offset_ + 2 > length_) {
+    if (length_ < 2 || offset_ > length_ - 2) {
       return OTS_FAILURE();
     }
     std::memcpy(value, buffer_ + offset_, sizeof(uint16_t));
@@ -122,7 +121,7 @@ class Buffer {
   }
 
   bool ReadU24(uint32_t *value) {
-    if (offset_ + 3 > length_) {
+    if (length_ < 3 || offset_ > length_ - 3) {
       return OTS_FAILURE();
     }
     *value = static_cast<uint32_t>(buffer_[offset_]) << 16 |
@@ -133,7 +132,7 @@ class Buffer {
   }
 
   bool ReadU32(uint32_t *value) {
-    if (offset_ + 4 > length_) {
+    if (length_ < 4 || offset_ > length_ - 4) {
       return OTS_FAILURE();
     }
     std::memcpy(value, buffer_ + offset_, sizeof(uint32_t));
@@ -147,7 +146,7 @@ class Buffer {
   }
 
   bool ReadR64(uint64_t *value) {
-    if (offset_ + 8 > length_) {
+    if (length_ < 8 || offset_ > length_ - 8) {
       return OTS_FAILURE();
     }
     std::memcpy(value, buffer_ + offset_, sizeof(uint64_t));
diff --git a/gfx/ots/src/stat.cc b/gfx/ots/src/stat.cc
index f6f65fdf60..0eeaffb1c6 100644
--- a/gfx/ots/src/stat.cc
+++ b/gfx/ots/src/stat.cc
@@ -48,10 +48,6 @@ bool OpenTypeSTAT::Parse(const uint8_t* data, size_t length) {
     this->minorVersion = 2;
   }
 
-  if (this->designAxisSize < sizeof(AxisRecord)) {
-    return Drop("Invalid designAxisSize");
-  }
-
   size_t headerEnd = table.offset();
 
   if (this->designAxisCount == 0) {
@@ -60,9 +56,13 @@ bool OpenTypeSTAT::Parse(const uint8_t* data, size_t length) {
       this->designAxesOffset = 0;
     }
   } else {
+    if (this->designAxisSize < sizeof(AxisRecord)) {
+      return Drop("Invalid designAxisSize");
+    }
     if (this->designAxesOffset < headerEnd ||
-        size_t(this->designAxesOffset) +
-          size_t(this->designAxisCount) * size_t(this->designAxisSize) > length) {
+        size_t(this->designAxesOffset) > length ||
+        size_t(this->designAxisCount) * size_t(this->designAxisSize) >
+          length - size_t(this->designAxesOffset)) {
       return Drop("Invalid designAxesOffset");
     }
   }
@@ -95,8 +95,9 @@ bool OpenTypeSTAT::Parse(const uint8_t* data, size_t length) {
     }
   } else {
     if (this->offsetToAxisValueOffsets < headerEnd ||
-        size_t(this->offsetToAxisValueOffsets) +
-          size_t(this->axisValueCount) * sizeof(uint16_t) > length) {
+        size_t(this->offsetToAxisValueOffsets) > length ||
+        size_t(this->axisValueCount) * sizeof(uint16_t) >
+          length - size_t(this->offsetToAxisValueOffsets)) {
       return Drop("Invalid offsetToAxisValueOffsets");
     }
   }
@@ -107,7 +108,9 @@ bool OpenTypeSTAT::Parse(const uint8_t* data, size_t length) {
     if (!table.ReadU16(&axisValueOffset)) {
       return Drop("Failed to read axis value offset");
     }
-    if (this->offsetToAxisValueOffsets + axisValueOffset > length) {
+    // We already checked that offsetToAxisValueOffsets doesn't exceed length,
+    // so this subtraction will not underflow.
+    if (axisValueOffset > length - this->offsetToAxisValueOffsets) {
       return Drop("Invalid axis value offset");
     }
     table.set_offset(this->offsetToAxisValueOffsets + axisValueOffset);